s3-winbindd: set the can_do_validation6 also for trusted domain

s3-winbindd: set the can_do_validation6 also for trusted domain

The flag can_do_validation6 was only set for the domain to which
winbindd is the member. Setting this flag in other domains (trusted
domain) if it's active directory domain is a good idea as it allow to do
level 6 validation also when winbindd is querying them directly.
(cherry picked from commit 05036fab0a9847219c73c0abd931a39fba0bccfd)

Address bug #8599 (WINBINDD_PAM_AUTH_CRAP returns invalid user session key).