config: mark unused callback parameters

The callback passed to git_config() must conform to a particular
interface. But most callbacks don't actually look at the extra "void
*data" parameter. Let's mark the unused parameters to make
-Wunused-parameter happy.

Note there's one unusual case here in get_remote_default() where we
actually ignore the "value" parameter. That's because it's only checking
whether the option is found at all, and not parsing its value.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ls-refs.c

@@ -136,7 +136,8 @@ static void send_possibly_unborn_head(struct ls_refs_data *data)
 	strbuf_release(&namespaced);
 }
 
-static int ls_refs_config(const char *var, const char *value, void *data)
+static int ls_refs_config(const char *var, const char *value,
+			  void *UNUSED(data))
 {
 	/*
 	 * We only serve fetches over v2 for now, so respect only "uploadpack"