net: thunderx: Enable TSO and checksum offloads for ipv6

Adding support for TSO and checksum hardware offloads for ipv6.

Signed-off-by: Thanneeru Srinivasulu <tsrinivasulu@cavium.com>
Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>