Take dup'd code for directmedia ACLs and make utility func

The same code was repeated in lots of different places, so I made a utility
fuction for it. This should make the merge in the v6-new branch easier.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@264905 65c4cc65-6c06-0410-ace0-fbb531ad65f3