On a failed bind, stop the callback from firing again

Not a problem but causes a slew of calls to upstream_bind_cb that will
all fail in the same way.

servers/lloadd/upstream.c

@@ -638,6 +638,7 @@ upstream_bind_cb( evutil_socket_t s, short what, void *arg )
     return;
 
 fail:
+    event_del( c->c_read_event );
     ber_free( ber, 1 );
     UPSTREAM_DESTROY(c);
 }