rr: docs - more details for sockname_mode param

(cherry picked from commit 86a5f81)

src/modules/rr/doc/rr_admin.xml

@@ -317,7 +317,8 @@ modparam("rr", "ignore_sips", 1)
 		<title><varname>sockname_mode</varname> (int)</title>
 		<para>
 		If set to 1, the Record-Route URI is built to contain socket name in 'sn'
-		parameter.
+		parameter and then it is used to lookup the local socket for Route header
+		processing.
 		</para>
 		<para>
 		<emphasis>