Enable new pfil(9) KPI ethernet filtering hooks to allow efficient packet filtering at packet ingress on mlx5en.
Note that the packets are filtered (and potentially dropped) *before* the driver has committed to (re)allocating an mbuf for the packet. Dropped packets are treated essentially the same as an error. Nothing is allocated, and the existing buffer is recycled. This allows us to drop packets at close to line rate with very little CPU use.