MINOR: protocol: uniformize protocol errors

Some protocols fail with "error blah [ip:port]" and other fail with
"[ip:port] error blah". All this already appears in a "starting" or
"binding" context after a proxy name. Let's choose a more universal
approach like below where the ip:port remains at the end of the line
prefixed with "for".

  [WARNING]  (18632) : Binding [binderr.cfg:10] for proxy http: cannot bind receiver to device 'eth2' (No such device) for [0.0.0.0:1080]
  [WARNING]  (18632) : Starting [binderr.cfg:10] for proxy http: cannot set MSS to 12 for [0.0.0.0:1080]
diff --git a/src/proto_uxdg.c b/src/proto_uxdg.c
index 7eb5a62..b0efe86 100644
--- a/src/proto_uxdg.c
+++ b/src/proto_uxdg.c
@@ -103,7 +103,7 @@
  uxdg_return:
 	if (msg && errlen) {
 		const char *path = ((struct sockaddr_un *)&listener->rx.addr)->sun_path;
-                snprintf(errmsg, errlen, "%s [%s]", msg, path);
+                snprintf(errmsg, errlen, "%s for [%s]", msg, path);
 	}
 	return err;
 }