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>

submodule.c

@@ -213,7 +213,8 @@ void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
 }
 
 /* Cheap function that only determines if we're interested in submodules at all */
-int git_default_submodule_config(const char *var, const char *value, void *cb)
+int git_default_submodule_config(const char *var, const char *value,
+				 void *UNUSED(cb))
 {
 	if (!strcmp(var, "submodule.recurse")) {
 		int v = git_config_bool(var, value) ?