add the challenge-realm option with some docs.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@9619 d0543943-73ff-0310-b7d9-9358b9ac24b2

conf/sip_profiles/internal.xml

@@ -142,6 +142,8 @@
     <!-- use stun when specified (default is true) -->
     <!-- set to true to have the profile determine stun is not useful and turn it off globally-->
     <!--<param name="stun-auto-disable" value="true"/>-->
+    <!-- Choose the realm challenge key. Default is auto_to -->
+    <!--<param name="challenge-realm" value="auto_from|auto_to|<hardcoded_val>"/>-->
   </settings>
 </profile>