s3:winbindd: Resolve dc name using CLDAP also for ROLE_IPA_DC

s3:winbindd: Resolve dc name using CLDAP also for ROLE_IPA_DC

server role ROLE_IPA_DC (introduced in e2d5b4d) needs special handling
in dcip_check_name().  We should resolve the DC name using:
- CLDAP in dcip_check_name_ads()
instead of:
- NETBIOS in nbt_getdc() that fails if Windows is not providing netbios.

The impacted environment has:

domain->alt_name = example.com
domain->active_directory = 1
security = USER
server role = ROLE_IPA_DC

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15891

Signed-off-by: Pavel Filipenský <pfilipensky@samba.org>
Signed-off-by: Andreas Schneider <asn@samba.org>
Pair-programmed-with: Andreas Schneider <asn@samba.org>

Reviewed-by: Alexander Bokovoy <ab@samba.org>