s3-winbindd: let winbind try to use samlogon validation level 6. (bug #7945)

s3-winbindd: let winbind try to use samlogon validation level 6. (bug #7945)

The benefit of this that it makes us more robust to secure channel resets
triggered from tools outside the winbind process. Long term we need to have a
shared tdb secure channel store though as well.

Guenther

Signed-off-by: Stefan Metzmacher <metze@samba.org>
(similar to commit f60398d7b20869d7b09d81854f3727fdcd897430)
(similar to commit 7add712498fe93603b1bffff2c633e097ce8fbdf)
(cherry picked from commit a5b388fc5ea81868f09590e8b7674826315c348c)