FS-7309: [mod_sofia] Allow removal of User-Agent header

In certain deployments it might be desirable to remove the User-Agent header from the SIP message.
Set the sofia profile parameter "user-agent-string" to "none" to suppress this header.

conf/vanilla/sip_profiles/internal-ipv6.xml

@@ -5,6 +5,7 @@
   <!-- http://wiki.freeswitch.org/wiki/Sofia_Configuration_Files -->
   <!--aliases are other names that will work as a valid profile name for this profile-->
   <settings>
+    <!-- Can be set to "_undef_" to remove the User-Agent header -->
     <!-- <param name="user-agent-string" value="FreeSWITCH Rocks!"/> -->
     <param name="debug" value="0"/>
     <param name="sip-trace" value="no"/>

conf/vanilla/sip_profiles/internal.xml

@@ -42,7 +42,10 @@
         bypass media after an attended transfer.
     -->
     <!--<param name="media-option" value="bypass-media-after-att-xfer"/>-->
+
+    <!-- Can be set to "_undef_" to remove the User-Agent header -->
     <!-- <param name="user-agent-string" value="FreeSWITCH Rocks!"/> -->
+
     <param name="debug" value="0"/>
     <!-- If you want FreeSWITCH to shutdown if this profile fails to load, uncomment the next line. -->
     <!-- <param name="shutdown-on-fail" value="true"/> -->