This is needed because tcpv6_prot has to point to the same place tcp_prot points,
as they share the same accounting variables.

This fixes a bug noticed by David Miller when using the ipv6_mapped functionality,
thanks David!
Signed-off-by: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
Signed-off-by: David S. Miller <davem@redhat.com>