Driver: Vmxnet3: Copy TCP header to mapped frame for IPv6 packets

Allows for packet parsing to be done by the fast path. This performance
optimization already exists for IPv4. Add similar logic for IPv6.

Signed-off-by: Amitabha Banerjee <banerjeea@vmware.com>
Signed-off-by: Shrikrishna Khare <skhare@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>