xfs: add tracing to high level transaction operations

Because currently we have no idea what the transaction context we
are operating in is, and I need to know that information to track
down bugs in multiple log item joins to transactions.

Signed-Off-By: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>