res_fax.c, res_fax_spandsp.c: Misc deadlock fixes.

res_fax.c, res_fax_spandsp.c: Misc deadlock fixes.

* Fixed locking inconsistency in fax_gateway_start() when calling the
gateway technology start_session callback.  The callback was called with
and without the channel lock held.  Calling the callback with the channel
lock held could deadlock in spandsp_fax_gateway_start() which calls
ast_channel_get_t38_state().

* Fixed deadlock potential in fax_detect_framehook() when calling
ast_channel_make_compatible().

ASTERISK-26203
Reported by: Etienne Lessard

ASTERISK-24822
Reported by: David Brillert

ASTERISK-22732
Reported by: Richard Mudgett

Change-Id: I5a7b8e9e7b198802df06dff0ea48d96bd6d7b912