Add the missing part of r400140

When the patch to add retry-on-forbidden-response was committed, part
of the patch for chan_sip was not committed which caused the feature to
be entirely nonfunctional. This corrects the code in question.

(closes issue ASTERISK-17138)
Review: https://reviewboard.asterisk.org/r/2874
........

Merged revisions 405033 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@405081 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -23390,6 +23390,13 @@ static int handle_response_register(struct sip_pvt *p, int resp, const char *res
 		}
 		break;
 	case 403:	/* Forbidden */
+		if (global_reg_retry_403) {
+			ast_log(LOG_NOTICE, "Treating 403 response to REGISTER as non-fatal for %s@%s\n",
+				p->registry->username, p->registry->hostname);
+			ast_string_field_set(r, nonce, "");
+			ast_string_field_set(p, nonce, "");
+			break;
+		}
 		ast_log(LOG_WARNING, "Forbidden - wrong password on authentication for REGISTER for '%s' to '%s'\n", p->registry->username, p->registry->hostname);
 		AST_SCHED_DEL_UNREF(sched, r->timeout, registry_unref(r, "reg ptr unref from handle_response_register 403"));
 		r->regstate = REG_STATE_NOAUTH;