PJSIP: Update transport method documentation

This updates the documentation for the 'method' configuration option to
be more verbose about the behaviors of values 'unspecified' and
'default'. They do exactly the same thing which is to select the
default as defined by PJSIP which is currently TLSv1.

Review: https://reviewboard.asterisk.org/r/4264/
........

Merged revisions 430145 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@430146 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_pjsip.c

@@ -875,8 +875,12 @@
 					<synopsis>Method of SSL transport (TLS ONLY)</synopsis>
 					<description>
 						<enumlist>
-							<enum name="default" />
-							<enum name="unspecified" />
+							<enum name="default">
+								<para>The default as defined by PJSIP. This is currently TLSv1, but may change with future releases.</para>
+							</enum>
+							<enum name="unspecified">
+								<para>This option is equivalent to setting 'default'</para>
+							</enum>
 							<enum name="tlsv1" />
 							<enum name="sslv2" />
 							<enum name="sslv3" />