net/mlx5: support matching on VXLAN reserved field

net/mlx5: support matching on VXLAN reserved field

This adds matching on the reserved field of VXLAN
header (the last 8-bits). The capability from rdma-core
is detected by creating a dummy matcher using misc5
when the device is probed.

For non-zero groups and FDB domain, the capability is
detected from rdma-core, meanwhile for NIC domain group
zero it's relying on the HCA_CAP from FW.

Signed-off-by: Rongwei Liu <rongweil@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Acked-by: Raslan Darawsheh <rasland@nvidia.com>