xfs: push down inactive transaction mgmt for ifree

Push the inode free work performed during xfs_inactive() down into
a new xfs_inactive_ifree() helper. This clears xfs_inactive() from
all inode locking and transaction management more directly
associated with freeing the inode xattrs, extents and the inode
itself.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>