smbd: Add share mode flags

This will contain a summary of the "most restrictive" share mode and
lease, i.e. intersection of all share_access entries and the union of
all access_mask and leases in the share mode array. This way
open_mode_check in the non-conflicting case will only have to look at
the summary and not walk the share mode array.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
