net/mlx5: support represented port item in flow rules

net/mlx5: support represented port item in flow rules

Add support for represented_port item in pattern. And if the spec and mask
both are NULL, translate function will not add source vport to matcher.

For example, testpmd starts with PF, VF-rep0 and VF-rep1, below command
will redirect packets from VF0 and VF1 to wire:
testpmd> flow create 0 ingress transfer group 0 pattern eth /
represented_port / end actions represented_port ethdev_id is 0 / end

Signed-off-by: Sean Zhang <xiazhang@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>