transport: Remove echo in transport selection

Do not echo the selected transport to avoid stray and confusing
messages in the output of OpenOCD. For example, the "swd" line here:

  Open On-Chip Debugger 0.12.0+dev-00559-ge02f6c1b9-dirty
  Licensed under GNU GPL v2
  For bug reports, read
  	http://openocd.org/doc/doxygen/bugs.html
  swd
  Info : Listening on port 6666 for tcl connections
  Info : Listening on port 4444 for telnet connections

While at it, fix some small documentation style issues.

Change-Id: Ie85426c441289bbaa35615dbb7b53f0b5c46cfc0
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/8217
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins

doc/openocd.texi

@@ -3693,20 +3693,18 @@ displays the names of the transports supported by this
 version of OpenOCD.
 @end deffn
 
-@deffn {Command} {transport select} @option{transport_name}
+@deffn {Command} {transport select} [transport_name]
 Select which of the supported transports to use in this OpenOCD session.
 
 When invoked with @option{transport_name}, attempts to select the named
-transport.  The transport must be supported by the debug adapter
+transport. The transport must be supported by the debug adapter
 hardware and by the version of OpenOCD you are using (including the
 adapter's driver).
-
-If no transport has been selected and no @option{transport_name} is
-provided, @command{transport select} auto-selects the first transport
-supported by the debug adapter.
-
-@command{transport select} always returns the name of the session's selected
-transport, if any.
+When invoked with no transport name:
+@itemize @minus
+@item if no transport has been selected yet, it auto-selects the first transport supported by the debug adapter
+@item it returns the name of the session's selected transport
+@end itemize
 @end deffn
 
 @subsection JTAG Transport

src/transport/transport.c

@@ -278,7 +278,6 @@ COMMAND_HANDLER(handle_transport_select)
 	if (session) {
 		if (!strcmp(session->name, CMD_ARGV[0])) {
 			LOG_WARNING("Transport \"%s\" was already selected", session->name);
-			command_print(CMD, "%s", session->name);
 			return ERROR_OK;
 		}
 		command_print(CMD, "Can't change session's transport after the initial selection was made");
@@ -301,7 +300,6 @@ COMMAND_HANDLER(handle_transport_select)
 			int retval = transport_select(CMD_CTX, CMD_ARGV[0]);
 			if (retval != ERROR_OK)
 				return retval;
-			command_print(CMD, "%s", session->name);
 			return ERROR_OK;
 		}
 	}