net/mlx5: prepare meson build for adding E-Switch VXLAN

net/mlx5: prepare meson build for adding E-Switch VXLAN

This patch updates meson.build before adding E-Switch VXLAN
encapsulation/decapsulation hardware offload support.
E-Switch rules are controlled via tc Netilnk commands,
so we need to include tc related headers, and check for
some tunnel specific key definitions.

Suggested-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Yongseok Koh <yskoh@mellanox.com>