net/mlx5e: Listen to ARP events to update IPsec L2 headers in tunnel mode

In IPsec packet offload mode all header manipulations are performed by
hardware, which is responsible to add/remove L2 header with source and
destinations MACs.

CX-7 devices don't support offload of in-kernel routing functionality,
as such HW needs external help to fill other side MAC as it isn't
available for HW.

As a solution, let's listen to neigh ARP updates and reconfigure IPsec
rules on the fly once new MAC data information arrives.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>