config: add options parameter to git_config_from_mem

The underlying config parser knows how to handle a
config_options struct, but git_config_from_mem() always
passes NULL. Let's allow our callers to specify the options
struct.

We could add a "_with_options" variant, but since there are
only a handful of callers, let's just update them to pass
NULL.

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

submodule-config.c

@@ -561,7 +561,7 @@ static const struct submodule *config_from(struct submodule_cache *cache,
 	parameter.gitmodules_oid = &oid;
 	parameter.overwrite = 0;
 	git_config_from_mem(parse_config, CONFIG_ORIGIN_SUBMODULE_BLOB, rev.buf,
-			config, config_size, &parameter);
+			config, config_size, &parameter, NULL);
 	strbuf_release(&rev);
 	free(config);