net/mlx5: Bridge, implement infrastructure for VLAN protocol change

Current implementation only supports 802.1Q VLAN Ethernet protocol. That
protocol type is assumed by default and
SWITCHDEV_ATTR_ID_BRIDGE_VLAN_PROTOCOL notification is ignored. To prepare
for supporting 802.1ad protocol in following patches implement the
necessary infrastructure to allow the user to dynamically change the VLAN
protocol:

- Handle SWITCHDEV_ATTR_ID_BRIDGE_VLAN_PROTOCOL notification by flushing
FDB and re-creating VLAN modify header actions with new protocol. In this
patch the only allowed dynamic VLAN protocol value is ETH_P_8021Q.

- Save current VLAN protocol in per-bridge instance variable. Use the
dynamic variable instead of hardcoded values in mlx5 bridge code. Create
VLAN flow groups and flows based on current mlx5_esw_bridge->vlan_proto
value instead of assuming 802.1Q ethertype.

- Extract common flow group creation code into dedicated functions in order
to be reused for creating QinQ groups in following patches.

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>