MINOR: listener: make sock_find_compatible_fd() check the socket type

sock_find_compatible_fd() can now access the protocol via the receiver
hence it can access its socket type and know whether the receiver has
dgram or stream sockets, so we don't need to hack around AF_CUST_UDP*
anymore there.
diff --git a/src/sock.c b/src/sock.c
index 8bdc3ea..3e7ba70 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -366,10 +366,7 @@
 	if (!l->rx.proto->addrcmp)
 		return -1;
 
-	/* WT: this is not the right way to do it, it is temporary for the
-	 *     transition to receivers.
-	 */
-	if (l->rx.addr.ss_family == AF_CUST_UDP4 || l->rx.addr.ss_family == AF_CUST_UDP6)
+	if (l->rx.proto->sock_type == SOCK_DGRAM)
 		options |= SOCK_XFER_OPT_DGRAM;
 
 	if (l->options & LI_O_FOREIGN)