mlxsw: reg: Add egr_et_set field to SPVID

SPVID.egr_et_set=1 means that when VLAN is pushed at ingress (for untagged
packets or for QinQ push mode) then the EtherType is decided at the egress
port.

The next patches will use this field for VxLAN devices (tunnel port) in
order to allow using dual VxLAN bridges (802.1d and 802.1ad at the same
time).

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