nvmet: add a clear_ids attribute for passthru targets

If the clear_ids attribute is set to true, the EUI/GUID/UUID is cleared
for the passthru target.  By default, loop targets will set clear_ids to
true.

This resolves an issue where a connect to a passthru target fails when
using a trtype of 'loop' because EUI/GUID/UUID is not unique.

Fixes: 2079f41e ("nvme: check that EUI/GUID/UUID are globally unique")
Signed-off-by: Alan Adamson <alan.adamson@oracle.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>