misc: change xfs_io -c swapext to exchangerange

misc: change xfs_io -c swapext to exchangerange

Update the swapext command to use exchangerange as part of severing the
connection between the two ioctls.

Flags changed:

-h (only exchange written extents) is now -w.

-a (atomic mode) is always enabled now.

-e (to eof) is now the default; -l (length) disables this flag.

-u (unconditonal swap) is inverted to -c (commit only if fresh).

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