net/mlx5e: Rename VLAN related variables and functions

Rename VLAN related symbols to better reflect the fact that they
are associated to C-tag VLAN.

Signed-off-by: Gal Pressman <galp@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>