res_pjsip_t38: Add the framehook to the channel only on first INVITE.

The check for determining whether the T.38 framehook should be added to
the channel or not has now been changed to guarantee adding only occurs
on the first incoming or outgoing INVITE.
........

Merged revisions 403258 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403259 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_pjsip_t38.c

@@ -446,8 +446,10 @@ static void t38_attach_framehook(struct ast_sip_session *session)
 		.event_cb = t38_framehook,
 	};
 
-	if (!session->channel || (ast_channel_state(session->channel) == AST_STATE_UP) ||
-	    !session->endpoint->media.t38.enabled) {
+	/* Only attach the framehook on the first outgoing INVITE or the first incoming INVITE */
+	if ((session->inv_session->state != PJSIP_INV_STATE_NULL &&
+		session->inv_session->state != PJSIP_INV_STATE_INCOMING) ||
+		!session->endpoint->media.t38.enabled) {
 		return;
 	}