Btrfs: enhance leak debug checker for extent state and extent buffer

This prints out eb->bflags since it contains some useful information,
e.g. whether eb is dirty.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>