s3/libsmb: check the negative-conn-cache in resolve_ads()

s3/libsmb: check the negative-conn-cache in resolve_ads()

This way we throw away blacklisted servers right away when learning about them
from the DNS SRV query.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14981

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Autobuild-User(master): Günther Deschner <gd@samba.org>
Autobuild-Date(master): Wed Jul 30 10:10:21 UTC 2025 on atb-devel-224

(cherry picked from commit c1ee6fe9a489a8923d607e14d26768935a398849)