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

MACsec driver marks Tx packets for device offload using a dedicated
skb_metadata_dst which holds a 64 bits SCI number.
A previously set rule will match on this number so the correct SA is used
for the MACsec operation.
As device driver can only provide 32 bits of metadata to flow tables,
need to used a mapping from 64 bit to 32 bits marker or id,
which is can be achieved by provide a 32 bit unique flow id in the
control path, and used a hash table to map 64 bit to the unique id in the
datapath.

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>