net/mlx5e: Implement MACsec Rx data path using MACsec skb_metadata_dst

MACsec driver need to distinguish to which offload device the MACsec
is target to, in order to handle them correctly.
This can be done by attaching a metadata_dst to a SKB with a SCI,
when there is a match on MACsec rule.
To achieve that, there is a map between fs_id to SCI, so for each RX SC,
there is a unique fs_id allocated when creating RX SC.
fs_id passed to device driver as metadata for packets that passed Rx
MACsec offload to aid the driver to retrieve the matching SCI.

Signed-off-by: Lior Nahmanson <liorna@nvidia.com>
Reviewed-by: Raed Salem <raeds@nvidia.com>
Signed-off-by: Raed Salem <raeds@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>