cxgbe(4): Stop and restart the atid allocator with the LLD.

atids are used by both filters and TOE and the atid table is in the base
driver (LLD). New atids cannot be allocated when the allocator is
stopped but existing ones can still be freed. It is expected that the
owners of outstanding atids will release them in their own stop
processing, before the adapter is restarted.

MFC after: 1 month
Sponsored by: Chelsio Communications