net/mlx5: add L2-L4 pattern items to switch flow rules

net/mlx5: add L2-L4 pattern items to switch flow rules

This enables flow rules to explicitly match supported combinations of
Ethernet, IPv4, IPv6, TCP and UDP headers at the switch level.

Testpmd example:

- Dropping TCPv4 traffic with a specific destination on port ID 2:

  flow create 2 ingress transfer pattern eth / ipv4 / tcp dst is 42 / end
     actions drop / end

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>