gossip: Do not log anything, it breaks a daemon connection!

This came up while debugging the gossip daemon breaking upon calling
`getroute`. It turns out that log was still writing to stdout, but
stdout had been reused for an inter-daemon socket, which would
break...

lightningd/gossip/gossip.c

@@ -529,7 +529,9 @@ int main(int argc, char *argv[])
 						 SECP256K1_CONTEXT_SIGN);
 
 	daemon = tal(NULL, struct daemon);
-	log_book = new_log_book(daemon, 2 * 1024 * 1024, LOG_INFORM);
+	/* Do not log absolutely anything, stdout is now a socket
+	 * connected to some other daemon. */
+	log_book = new_log_book(daemon, 2 * 1024 * 1024, LOG_BROKEN + 1);
 	base_log =
 	    new_log(daemon, log_book, "lightningd_gossip(%u):", (int)getpid());
 	daemon->rstate = new_routing_state(daemon, base_log);