BUG/MEDIUM: resolvers: Don't set an address-less server as UP

when a server status is updated based on a SRV item, it is always set to UP,
regardless it has an IP address defined or not. For instance, if only a SRV
item is received, with no additional record, only the server hostname is
defined. We must wait to have an IP address to set the server as UP.

This patch must be backported as far as 2.2.
diff --git a/src/resolvers.c b/src/resolvers.c
index 96431f4..859189d 100644
--- a/src/resolvers.c
+++ b/src/resolvers.c
@@ -659,8 +659,8 @@
 						send_log(srv->proxy, LOG_NOTICE, "%s", msg);
 				}
 
-				/* now we have an IP address associated to this server, we can update its status */
-				snr_update_srv_status(srv, 0);
+				/* Update the server status */
+				snr_update_srv_status(srv, (srv->addr.ss_family != AF_INET && srv->addr.ss_family != AF_INET6));
 
 				srv->svc_port = item->port;
 				srv->flags   &= ~SRV_F_MAPPORTS;