xfs: refactor xlog_recover_commit_trans

Merge the call to xlog_recover_reorder_trans and the loop over the
recovery items from xlog_recover_do_trans into xlog_recover_commit_trans,
and keep the switch statement over the log item types as a separate helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>