IAX2 encryption regression

IAX2 encryption regression

The IAX2 Call Token security patch inadvertently broke the use of
encryption due to the reorganization of code in the socket_process()
function.  When encryption is used, an incoming full frame must first
be decrypted before the information elements can be parsed.  The
security release mistakenly moved IE parsing before decryption in
order to process the new Call Token IE.  To resolve this, decryption
of full frames is once again done before looking into the frame.  This
involves searching for an existing callno, checking the pvt to see if
encryption is turned on, and decrypting the packet before the internal
fields of the full frame are accessed.

associated with AST-2009-006

(closes issue #15834)
Reported by: karesmakro
Patches:
      iax2_encryption_fix_1.4.diff uploaded by dvossel (license 671)
Tested by: dvossel, karesmakro

Review: https://reviewboard.asterisk.org/r/355/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@217806 65c4cc65-6c06-0410-ace0-fbb531ad65f3