channels/chan_sip: Set cause code to 44 on RTP timeout

To quote Olle:

"When issuing a hangup due to RTP timeouts the cause code is not set. I have
selected 44 based on Cisco's implementation..."

ASTERISK-25135 #close
Reported by: Olle Johansson
patches:
  rtp-timeout-cause-1.8.diff uploaded by Olle Johansson (License 5267)

Change-Id: Ia62100c55077d77901caee0bcae299f8dc7375fc

channels/chan_sip.c

@@ -28811,7 +28811,8 @@ static int check_rtp_timeout(struct sip_pvt *dialog, time_t t)
 					ast_channel_name(dialog->owner), (long) (t - dialog->lastrtprx));
 				send_session_timeout(dialog->owner, "RTPTimeout");
 
-				/* Issue a softhangup */
+				/* Issue a softhangup - cause 44 (as used by Cisco for RTP timeouts) */
+				ast_channel_hangupcause_set(dialog->owner, AST_CAUSE_REQUESTED_CHAN_UNAVAIL);
 				ast_softhangup_nolock(dialog->owner, AST_SOFTHANGUP_DEV);
 				ast_channel_unlock(dialog->owner);
 				/* forget the timeouts for this call, since a hangup