close and close due to revoke(2)-like operation.
A new FLASTCLOSE flag indicates that this is last close. FREVOKE is
set for revokes, and FNONBLOCK is also set, same as is already done
for VOP_CLOSE() call from vgonel().
The flags reuse user open(2) flags which are never stored in f_flag,
to not consume bit space in the ABI visible way. Assert this with the
static check.
Requested and reviewed by: bde
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
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