framehooks: Add callback for determining if a hook is consuming frames of a specific type.

In the past framehooks have had no capability to determine what frame types a hook
is actually interested in consuming. This has meant that code has had to assume they
want all frames, thus preventing native bridging.

This change adds a callback which allows a framehook to be queried for whether it
is consuming a frame of a specific type. The native RTP bridging module has also
been updated to take advantange of this, allowing native bridging to occur when
previously it would not.

ASTERISK-23497 #comment Reported by: Etienne Lessard
ASTERISK-23497 #close

Review: https://reviewboard.asterisk.org/r/3522/
........

Merged revisions 413650 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@413651 65c4cc65-6c06-0410-ace0-fbb531ad65f3