mlx4: use dummy Rx queues when non-pow2 number requested

mlx4: use dummy Rx queues when non-pow2 number requested

When using RSS, the number of rxqs has to be a power of two.
This is a problem because there is no API in DPDK that makes
the application aware of that.

A good compromise is to allow the application to request a
number of rxqs that is not a power of 2, but having inactive
queues that will never receive packets. In this configuration,
a warning will be issued to users to let them know that
this is not an optimal configuration.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>