tcpv6: combine tcp_v6_send_(reset|ack)

tcpv6: combine tcp_v6_send_(reset|ack)

$ codiff tcp_ipv6.o.old tcp_ipv6.o.new
net/ipv6/tcp_ipv6.c:
  tcp_v6_md5_hash_hdr | -144
  tcp_v6_send_ack     | -585
  tcp_v6_send_reset   | -540
 3 functions changed, 1269 bytes removed, diff: -1269

net/ipv6/tcp_ipv6.c:
  tcp_v6_send_response | +791
 1 function changed, 791 bytes added, diff: +791

tcp_ipv6.o.new:
 4 functions changed, 791 bytes added, 1269 bytes removed, diff: -478

I choose to leave the reset related netns comment in place (not
the one that is killed) as I cannot understand its English so
it's a bit hard for me to evaluate its usefulness :-).

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>