mlxsw: spectrum_nve_vxlan: Add support for Q-in-VNI for Spectrum-2 ASIC

On Spectrum-2, the default setting is not to push VLAN to the decapsulated
packet. This is controlled by SPVTR.ipvid_mode.
Set SPVTR.ipvid_mode to always push VLAN.
Without this setting, Spectrum-2 overtakes the VLAN tag of decapsulated
packet for bridging.

In addition, set SPVID register to use EtherType saved in
mlxsw_sp_nve_config when VLAN is pushed for the NVE tunnel.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>