net/mlx5: add necessary definitions for E-Switch VXLAN

net/mlx5: add necessary definitions for E-Switch VXLAN

This patch contains tc flower related and some other definitions
needed to implement VXLAN encapsulation/decapsulation hardware
offload support for E-Switch.

mlx5 driver dynamically creates and manages the VXLAN virtual
tunnel endpoint devices, the following definitions control
the parameters of these network devices:

- MLX5_VXLAN_PORT_MIN - minimal allowed UDP port for VXLAN device
- MLX5_VXLAN_PORT_MAX - maximal allowed UDP port for VXLAN device
- MLX5_VXLAN_DEVICE_PFX - name prefix of driver created VXLAN device

The mlx5 drivers creates the VXLAN devices with UDP port within
specified range, devices have the names with specified prefix,
followed by decimal digits of UDP port.

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