net/mlx5: Bridge, extract VLAN push/pop actions creation

Following patches in series need to re-create VLAN actions when user
changes VLAN protocol. Extract the code that creates VLAN push/pop actions
into dedicated function in order to be reused in next patch.

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