Help mitigate potential reinvite glare scenarios.

When Asterisk servers are set up back-to-back, and
direct media is to be used betweeen endpoints, it is
fairly common for the two Asterisk servers to send
direct media reinvites to each other simultaneously.
This results in 491s and ACKs being exchanged between
the servers. While the media eventually gets set up
properly, the problem is that there can be a noticeable
delay for the streams to stabilize.

This patch adds a new directmedia option called "outgoing".
With this set, an immediate direct media reinvite will only
be sent if the call direction is outgoing. For incoming
dialogs, an immediate direct media reinvite will not be sent,
but further "reactionary" direct media reinvites may be sent.

For those who are having some deja vu, that's because this
patch was originally committed to trunk since there is a
new configuration option added. After seeing a bug report
about audio being slow to set up on SIP calls, it became
apparent that this patch would be the best solution for
resolving the issue. The patch is unintrusive and will
have no effect unless the option is explicitly enabled.

(closes issue AST-896)
reported by Thomas Arimont

(closes issue ASTERISK-19857)
reported by Matt Jordan



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@370618 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/sip/include/sip.h

@@ -357,9 +357,10 @@
 
 
 #define SIP_PAGE3_SNOM_AOC               (1 << 0)  /*!< DPG: Allow snom aoc messages */
+#define SIP_PAGE3_DIRECT_MEDIA_OUTGOING  (1 << 1)  /*!< DP: Only send direct media reinvites on outgoing calls */
 
 #define SIP_PAGE3_FLAGS_TO_COPY \
-	(SIP_PAGE3_SNOM_AOC)
+	(SIP_PAGE3_SNOM_AOC | SIP_PAGE3_DIRECT_MEDIA_OUTGOING)
 
 /*@}*/