Implement the TLS tx offload data path according to the
requirements of the TLS generic NIC offload infrastructure.

Special metadata ethertype is used to pass information to
the hardware.
Signed-off-by: NIlya Lesokhin <ilyal@mellanox.com>
Signed-off-by: NBoris Pismenny <borisp@mellanox.com>
Acked-by: NSaeed Mahameed <saeedm@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>