X509V3_get_d2i.pod: use I<> for arguments and remove B<> around NULL

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from openssl#17724)

doc/man3/X509V3_get_d2i.pod

@@ -39,37 +39,37 @@ X509_REVOKED_get0_extensions - X509 extension decode and encode functions
 
 =head1 DESCRIPTION
 
-X509V3_get_d2i() looks for an extension with OID B<nid> in the extensions
-B<x> and, if found, decodes it. If B<idx> is B<NULL> then only one
+X509V3_get_d2i() looks for an extension with OID I<nid> in the extensions
+I<x> and, if found, decodes it. If I<idx> is NULL then only one
 occurrence of an extension is permissible otherwise the first extension after
-index B<*idx> is returned and B<*idx> updated to the location of the extension.
-If B<crit> is not B<NULL> then B<*crit> is set to a status value: -2 if the
-extension occurs multiple times (this is only returned if B<idx> is B<NULL>),
+index I<*idx> is returned and I<*idx> updated to the location of the extension.
+If I<crit> is not NULL then I<*crit> is set to a status value: -2 if the
+extension occurs multiple times (this is only returned if I<idx> is NULL),
 -1 if the extension could not be found, 0 if the extension is found and is
 not critical and 1 if critical. A pointer to an extension specific structure
-or B<NULL> is returned.
+or NULL is returned.
 
-X509V3_add1_i2d() adds extension B<value> to STACK B<*x> (allocating a new
-STACK if necessary) using OID B<nid> and criticality B<crit> according
-to B<flags>.
+X509V3_add1_i2d() adds extension I<value> to STACK I<*x> (allocating a new
+STACK if necessary) using OID I<nid> and criticality I<crit> according
+to I<flags>.
 
 X509V3_EXT_d2i() attempts to decode the ASN.1 data contained in extension
-B<ext> and returns a pointer to an extension specific structure or B<NULL>
+I<ext> and returns a pointer to an extension specific structure or NULL
 if the extension could not be decoded (invalid syntax or not supported).
 
-X509V3_EXT_i2d() encodes the extension specific structure B<ext>
-with OID B<ext_nid> and criticality B<crit>.
+X509V3_EXT_i2d() encodes the extension specific structure I<ext>
+with OID I<ext_nid> and criticality I<crit>.
 
 X509_get_ext_d2i() and X509_add1_ext_i2d() operate on the extensions of
-certificate B<x>, they are otherwise identical to X509V3_get_d2i() and
+certificate I<x>, they are otherwise identical to X509V3_get_d2i() and
 X509V3_add_i2d().
 
 X509_CRL_get_ext_d2i() and X509_CRL_add1_ext_i2d() operate on the extensions
-of CRL B<crl>, they are otherwise identical to X509V3_get_d2i() and
+of CRL I<crl>, they are otherwise identical to X509V3_get_d2i() and
 X509V3_add_i2d().
 
 X509_REVOKED_get_ext_d2i() and X509_REVOKED_add1_ext_i2d() operate on the
-extensions of B<X509_REVOKED> structure B<r> (i.e for CRL entry extensions),
+extensions of B<X509_REVOKED> structure I<r> (i.e for CRL entry extensions),
 they are otherwise identical to X509V3_get_d2i() and X509V3_add_i2d().
 
 X509_get0_extensions(), X509_CRL_get0_extensions() and
@@ -79,9 +79,9 @@ of a certificate a CRL or a CRL entry respectively.
 =head1 NOTES
 
 In almost all cases an extension can occur at most once and multiple
-occurrences is an error. Therefore, the B<idx> parameter is usually B<NULL>.
+occurrences is an error. Therefore, the I<idx> parameter is usually NULL.
 
-The B<flags> parameter may be one of the following values.
+The I<flags> parameter may be one of the following values.
 
 B<X509V3_ADD_DEFAULT> appends a new extension only if the extension does
 not already exist. An error is returned if the extension does already
@@ -100,15 +100,15 @@ B<X509V3_ADD_KEEP_EXISTING> appends a new extension only if the extension does
 not already exist. An error B<is not> returned if the extension does already
 exist.
 
-B<X509V3_ADD_DELETE> extension B<nid> is deleted: no new extension is added.
+B<X509V3_ADD_DELETE> extension I<nid> is deleted: no new extension is added.
 
-If B<X509V3_ADD_SILENT> is ored with B<flags>: any error returned will not
+If B<X509V3_ADD_SILENT> is ored with I<flags>: any error returned will not
 be added to the error queue.
 
 The function X509V3_get_d2i() and its variants
-will return B<NULL> if the extension is not
+will return NULL if the extension is not
 found, occurs multiple times or cannot be decoded. It is possible to
-determine the precise reason by checking the value of B<*crit>.
+determine the precise reason by checking the value of I<*crit>.
 
 =head1 SUPPORTED EXTENSIONS
 
@@ -198,15 +198,15 @@ The following extensions are used by certificate transparency, RFC6962
 =head1 RETURN VALUES
 
 X509V3_get_d2i(), its variants, and X509V3_EXT_d2i() return
-a pointer to an extension specific structure or B<NULL> if an error occurs.
+a pointer to an extension specific structure or NULL if an error occurs.
 
 X509V3_add1_i2d() and its variants return 1 if the operation is successful
 and 0 if it fails due to a non-fatal error (extension not found, already exists,
 cannot be encoded) or -1 due to a fatal error such as a memory allocation
 failure.
 
 X509V3_EXT_i2d() returns a pointer to an B<X509_EXTENSION> structure
-or B<NULL> if an error occurs.
+or NULL if an error occurs.
 
 X509_get0_extensions(), X509_CRL_get0_extensions() and
 X509_REVOKED_get0_extensions() return a stack of extensions. They return