defaults: oomprotect sshd and local_unbound

Add sshd and local_unbound to the oom protected services.
syslogd is protected by default already, document it.

This was discussed on arch@, see
    https://lists.freebsd.org/archives/freebsd-arch/2023-November/000543.html

sshd is protected to be able to investigate and fix oom issues on systems
which don't have out-of-band console access.
local_unbound is protected as it may be enabled for local use and without
DNS a lot grinds to a halt (including sshd).

Relnotes:		yes
MFC after:		1 month
Differential Revision:	https://reviews.freebsd.org/D42544

libexec/rc/rc.conf

@@ -318,6 +318,7 @@ ggated_config="/etc/gg.exports"	# ggated(8) exports file.
 ggated_flags=""			# Extra parameters like which port to bind to.
 ctld_enable="NO"		# CAM Target Layer / iSCSI target daemon.
 local_unbound_enable="NO"	# Local caching DNS resolver
+local_unbound_oomprotect="YES"	# Don't kill local_unbound when swap space is exhausted.
 local_unbound_tls="NO"		# Use DNS over TLS
 blacklistd_enable="NO"		# Run blacklistd daemon (YES/NO).
 blacklistd_flags=""		# Optional flags for blacklistd(8).
@@ -364,6 +365,7 @@ pppoed_provider="*"		# Provider and ppp(8) config file entry.
 pppoed_flags="-P /var/run/pppoed.pid"	# Flags to pppoed (if enabled).
 pppoed_interface="em0"		# The interface that pppoed runs on.
 sshd_enable="NO"		# Enable sshd
+sshd_oomprotect="YES"		# Don't kill sshd when swap space is exhausted.
 sshd_program="/usr/sbin/sshd"	# path to sshd, if you want a different one.
 sshd_flags=""			# Additional flags for sshd.
 ftpd_enable="NO"		# Enable stand-alone ftpd.

share/man/man5/rc.conf.5

@@ -22,7 +22,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd September 18, 2023
+.Dd November 13, 2023
 .Dt RC.CONF 5
 .Os
 .Sh NAME
@@ -2318,6 +2318,12 @@ If set to
 run the
 .Xr syslogd 8
 daemon.
+Note, the
+.Va syslogd_oomprotect
+variable is set to
+.Dq Li YES
+by default in
+.Pa /etc/defaults/rc.conf .
 .It Va syslogd_program
 .Pq Vt str
 Path to
@@ -2381,6 +2387,12 @@ If set to
 run the
 .Xr unbound 8
 daemon as a local caching DNS resolver.
+Note, the
+.Va local_unbound_oomprotect
+variable is set to
+.Dq Li YES
+by default in
+.Pa /etc/defaults/rc.conf .
 .It Va nscd_enable
 .Pq Vt bool
 Set to
@@ -3840,6 +3852,12 @@ Set to
 to start
 .Xr sshd 8
 at system boot time.
+Note, the
+.Va sshd_oomprotect
+variable is set to
+.Dq Li YES
+by default in
+.Pa /etc/defaults/rc.conf .
 .It Va sshd_flags
 .Pq Vt str
 If