Add Record-Route for in-dialog NOTIFY as per RFC 6665.

etc/kamailio.cfg

@@ -574,10 +574,14 @@ route[WITHINDLG] {
 				setflag(FLT_ACC); # do accounting ...
 				setflag(FLT_ACCFAILED); # ... even if the transaction fails
 			}
-			if ( is_method("ACK") ) {
+			else if ( is_method("ACK") ) {
 				# ACK is forwarded statelessy
 				route(NATMANAGE);
 			}
+			else if ( is_method("NOTIFY") ) {
+				# Add Record-Route for in-dialog NOTIFY as per RFC 6665.
+				record_route();
+			}
 			route(RELAY);
 		} else {
 			if (is_method("SUBSCRIBE") && uri == myself) {