fuse2fs: disable renameat2

fuse2fs: disable renameat2

Apparently fuse munged rename and renameat2 together into the same
upcall, so we actually have to filter out nonzero flags because
otherwise we do a regular rename for a RENAME_EXCHANGE/WHITEOUT, which
is not what the user asked for.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/174553065177.1160461.684615549721279410.stgit@frogsfrogsfrogs
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
(cherry picked from commit b431abbc8fe0fd1de4e414aae3520c4c19411048)