cxgbe(4): fixes for netmap operation with only some queues active.

cxgbe(4): fixes for netmap operation with only some queues active.

- Only active netmap receive queues should be in the RSS lookup table.

- The RSS table should be restored for NIC operation when the last
  active netmap queue is switched off, not the first one.

- Support repeated netmap ON/OFF on a subset of the queues.  This works
  whether the the queues being enabled and disabled are the only ones
  active or not.  Some kring indexes have to be reset in the driver for
  the second case.

MFC after:	1 week
Sponsored by:	Chelsio Communications