cxgbe(4): Allow tunables that control the number of queues to be set to
'-n' to tell the driver to create _up to_ 'n' queues if enough cores are
available. For example, setting hw.cxgbe.nrxq10g="-32" will result in
16 queues if the system has 16 cores, 32 if it has 32.

There is no change in the default number of queues of any type.

MFC after: 1 week
Sponsored by: Chelsio Communications