res_fax.c: Fix deadlock potential in FAXOPT(faxdetect) framehook.

The fax_detect_framehook() has the potential to deadlock if an incoming
fax happens during the Playback or similar application.

* Fixed the potential deadlock by not calling ast_async_goto() with the
channel lock held.

* Made always eat the fax detection frame whether there is a fax extension
or not.

* Made only detach the framehook if we detected a fax and not on other
possible frames.

ASTERISK-26216
Reported by: Richard Mudgett

Change-Id: I99da35c26d1cd802626ffb4c1b4eb5b015581b6d