mlx5: support BIG TCP packets

mlx5 supports LSOv2.

IPv6 gro/tcp stacks insert a temporary Hop-by-Hop header
with JUMBO TLV for big packets.

We need to ignore/skip this HBH header when populating TX descriptor.

Note that ipv6_has_hopopt_jumbo() only recognizes very specific packet
layout, thus mlx5e_sq_xmit_wqe() is taking care of this layout only.

v7: adopt unsafe_memcpy() and MLX5_UNSAFE_MEMCPY_DISCLAIMER
v2: clear hopbyhop in mlx5e_tx_get_gso_ihs()
v4: fix compile error for CONFIG_MLX5_CORE_IPOIB=y

Signed-off-by: Coco Li <lixiaoyan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Cc: Saeed Mahameed <saeedm@nvidia.com>
Cc: Leon Romanovsky <leon@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>