framehooks: Re-iterate if framehook provides different frame.

Framehooks can be used in a reactive manner to execute specific logic
when a frame is received with a certain type and payload. Since it is
possible for framehooks to provide frames it was possible for this
reactive framehook to be unaware of frames it is looking for.

This change makes it so that when framehooks return a modified frame
the code will now re-iterate (from the beginning) and call any
previous framehooks that have not provided a modified frame themselves.

Review: https://reviewboard.asterisk.org/r/3046/
........

Merged revisions 404027 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@404028 65c4cc65-6c06-0410-ace0-fbb531ad65f3