cifs: Fix non-availability of dedup breaking generic/304

Deduplication isn't supported on cifs, but cifs doesn't reject it, instead
treating it as extent duplication/cloning.  This can cause generic/304 to go
silly and run for hours on end.

Fix cifs to indicate EOPNOTSUPP if REMAP_FILE_DEDUP is set in
->remap_file_range().

Note that it's unclear whether or not commit b073a080 is meant to cause
cifs to return an error if REMAP_FILE_DEDUP.

Fixes: b073a080 ("cifs: fix that return -EINVAL when do dedupe operation")
Cc: stable@vger.kernel.org
Suggested-by: Dave Chinner <david@fromorbit.com>
cc: Xiaoli Feng <fengxiaoli0714@gmail.com>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Darrick Wong <darrick.wong@oracle.com>
cc: fstests@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/3876191.1701555260@warthog.procyon.org.uk/


Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>