ipv6: Support new TSO without HBH

[gentoo-root]

Currently, BIG TCP IPv6 inserts a hop-by-hop extension header with a jumbo payload option to reflect the real length of the packet bigger than 65535 bytes. New kernels will drop this extension header and just calculate the packet length from skb->len, like it's currently done for BIG TCP IPv4.

Reflect the future kernel change in tcpdump and support parsing such packets.

Kernel ref: https://lore.kernel.org/netdev/[email protected]/