net/mlx5e: DCBNL fix min inline header size for dscp

When the trust state is set to dscp and the netdev is down, the inline
header size is not updated. When netdev is up, the inline header size
stays at L2 instead of IP.

Fix this issue by updating the private parameter when the netdev is in
down so that when netdev is up, it picks up the right header size.

Fixes: fbcb127e

 ("net/mlx5e: Support DSCP trust state ...")
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>