[gve] Set descriptor and completion ring sizes when creating queues

[gve] Set descriptor and completion ring sizes when creating queues

The "create TX queue" and "create RX queue" commands have fields for
the descriptor and completion ring sizes, which are currently left
unpopulated since they are not required for the original GQI-QPL
operating mode.

Populate these fields, and allow for the possibility that a transmit
completion ring exists (which will be the case when using the DQO
operating mode).

Signed-off-by: Michael Brown <mcb30@ipxe.org>