tag: use new advice API to check visibility

change the advise call in tag library from advise() to
advise_if_enabled() to construct an example of the usage of
the new API.

Signed-off-by: Heba Waly <heba.waly@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/tag.c b/builtin/tag.c
index e0a4c25..cc30d34 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -231,8 +231,9 @@ static void create_tag(const struct object_id *object, const char *object_ref,
 	if (type <= OBJ_NONE)
 		die(_("bad object type."));
 
-	if (type == OBJ_TAG && advice_nested_tag)
-		advise(_(message_advice_nested_tag), tag, object_ref);
+	if (type == OBJ_TAG)
+		advise_if_enabled(ADVICE_NESTED_TAG, _(message_advice_nested_tag),
+				  tag, object_ref);
 
 	strbuf_addf(&header,
 		    "object %s\n"