Fix remaining signedness errors

We can change the data type for 'size' but we have to cast len to size_t
for the comparisons with sizeof results.

src/wayland-server.c

@@ -202,7 +202,7 @@ wl_client_connection_data(int fd, uint32_t mask, void *data)
 		return 1;
 	}
 
-	while (len >= sizeof p) {
+	while ((size_t) len >= sizeof p) {
 		wl_connection_copy(connection, p, sizeof p);
 		opcode = p[1] & 0xffff;
 		size = p[1] >> 16;