IB/core: Do not notify GID change event of an unregistered device

IB/core: Do not notify GID change event of an unregistered device

When IB device is undergoing unregistration, the GID cache is always
cleaned up after all clients are unregistered with the below flow.

__ib_unregister_device()
  disable_device()
  ib_cache_cleanup_one()
    gid_table_cleanup_one()
      cleanup_gid_table_port()

There is no use in generating a GID change event at this stage, where
there is no active client of the device and device is nearly unregistered.

Link: https://lore.kernel.org/r/20191020065427.8772-4-leon@kernel.org
Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>