ipv6: tcp: consistently use MAX_TCP_HEADER

All other skbs allocated for TCP tx are using MAX_TCP_HEADER already.

MAX_HEADER can be too small for some cases (like eBPF based encapsulation),
so this can avoid extra pskb_expand_head() in lower stacks.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20220222031115.4005060-1-eric.dumazet@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>