net/mlx5e: Add function to get IPsec offload namespace

Add function to get namespace in different directions. It will be
extended for switchdev mode in later patch, but no functionality change
for now.

Signed-off-by: Jianbo Liu <jianbol@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/ac2982c34f1ed3288d4670cacfd7e1b87a8c96d9.1690802064.git.leon@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>