When a SIP peer unregisters set the expiry time back to 0 so that the 200 OK contains an expires of 0.

(closes issue #13599)
Reported by: hjourdain
Patches:
      chan_sip.c.diff uploaded by hjourdain (license 583)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@162738 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -8252,6 +8252,7 @@ static enum parse_register_result parse_register_contact(struct sip_pvt *pvt, st
 		peer->useragent[0] = '\0';
 		peer->sipoptions = 0;
 		peer->lastms = 0;
+		pvt->expiry = 0;
 
 		if (option_verbose > 2)
 			ast_verbose(VERBOSE_PREFIX_3 "Unregistered SIP '%s'\n", peer->name);