dm: do not forward ioctls from logical volumes to the underlying device

A logical volume can map to just part of underlying physical volume.
In this case, it must be treated like a partition.

Based on a patch from Alasdair G Kergon.

Cc: Alasdair G Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
static void trigger_event(struct work_struct *work)
{
	struct multipath *m =
		container_of(work, struct multipath, trigger_event);

	dm_table_event(m->ti->table);
}

static void trigger_event(struct work_struct *work)
{
	struct multipath *m =
		container_of(work, struct multipath, trigger_event);

	dm_table_event(m->ti->table);
}
