bridge_native_rtp.c: Fixup native_rtp_framehook()

* Fix framehook to test frame type for control frame.
* Made framehook exit early if frame type is not a control frame.
* Eliminated RAII_VAR in framehook.
* Use switch instead of else-if ladder for control frame handling.

Change-Id: Ia555fc3600bd85470e3c0141147dbe3ad07c1d18