Now that the generic btree code supports overlapping intervals, plug
in the rmap btree to this functionality.  We will need it to find
potential left neighbors in xfs_rmap_{alloc,free} later in the patch
set.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>