Fix syntax error.

gtests/net/packetdrill/packet_socket_linux.c

@@ -173,7 +173,7 @@ void packet_socket_set_filter(struct packet_socket *psock,
 			       ((u32)client_ether[4] << 8)  |
 			       ((u32)client_ether[5]));
 	bpfcode.filter[3].k = (((u32)client_ether[0] << 8)  |
-			       ((u32(client_ether[1]));
+			       ((u32)client_ether[1]));
 
 	if (debug_logging) {
 		int i;