common/sfc_efx/base: maintain RxQ counter in generic code

common/sfc_efx/base: maintain RxQ counter in generic code

The counter is incremented in generic efx_rx_qcreate(), but was
asserted and decremented in NIC family specific queue create and
destroy callbacks.  Move assert and decrement to generic functions
as well to make NIC family specific callbacks shorter.

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>