gossmap: add (and use) logging hook.

Default goes to stderr for LOG_UNUSUAL and higher.

We have to whitelist more cases in map_catchup so we don't spam the logs
with perfectly-expected (but ignored) messages though.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

devtools/topology.c

@@ -256,7 +256,7 @@ int main(int argc, char *argv[])
 		opt_usage_exit_fail("Expect 3 arguments");
 
 	tstart = time_mono();
-	map = gossmap_load(NULL, argv[1], NULL);
+	map = gossmap_load(NULL, argv[1], NULL, NULL);
 	if (!map)
 		err(1, "Loading gossip store %s", argv[1]);
 	tstop = time_mono();