xfs: remove xfs_da_args.attr_flags

xfs: remove xfs_da_args.attr_flags

Source kernel commit: 54275d8496f3e4764302cebc0e9517d950ba6589

This field only ever contains XATTR_{CREATE,REPLACE}, and it only goes
as deep as xfs_attr_set.  Remove the field from the structure and
replace it with an enum specifying exactly what kind of change we want
to make to the xattr structure.  Upsert is the name that we'll give to
the flags==0 operation, because we're either updating an existing value
or inserting it, and the caller doesn't care.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>