nbd: fix how we set bd_invalidated

nbd: fix how we set bd_invalidated

BugLink: https://bugs.launchpad.net/bugs/1822247
bd_invalidated is kind of a pain wrt partitions as it really only
triggers the partition rescan if it is set after bd_ops->open() runs, so
setting it when we reset the device isn't useful.  We also sporadically
would still have partitions left over in some disconnect cases, so fix
this by always setting bd_invalidated on open if there's no
configuration or if we've had a disconnect action happen, that way the
partition table gets invalidated and rescanned properly.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from fe1f9e6659ca6124f500a0f829202c7c902fab0c)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>