Fix a couple of bad races that can occur when a cxgbe interface is taken
down. The ingress queue lock was unused and has been removed as part of
these changes.

• An in-flight egress update from the SGE must be handled before the queue that requested it is destroyed. Wait for the update to arrive.

• Interrupt handlers must stop processing rx events for a queue before the queue is destroyed. Events that have not yet been processed should be ignored once the queue disappears.

MFC after: 1 week