res_fax: Resolve module reference leak caused by reserved sessions

Remove reference to module providing reserved session after
adding a reference to the final module.  This re-reference
is done to ensure that module references are correct even
if the final session selects a different module than the
reserved session.

ASTERISK-18923 #close
Reported by: Grigoriy Puzankin
Review: https://reviewboard.asterisk.org/r/4048/
........

Merged revisions 425405 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@425407 f38db490-d61c-443f-a65b-d21fe96a405b
res_fax: Fix reference leak caused by gateway sessions

Fax gateway session objects can be re-used, causing the
same gateway session to be added to faxregistry.container
more than once.  This change causes fax_session_new to
remove the reserved session from the container before
it's id is changed, ensuring it's possible for the
session to be freed.

ASTERISK-24392 #close
Reported by: Corey Farrell
Review: https://reviewboard.asterisk.org/r/4049/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@425457 f38db490-d61c-443f-a65b-d21fe96a405b