. export tcp_bind_hash
. use tcp_bind_hash in tcp_v6_get_port
. create tcp_v6_bind_conflict from code in tcp_v6_get_port, making
  it look more like tcp_v4_get_port
. create ipv6_rcv_saddr_equal to reduce the complexity in
  tcp_v6_bind_conflict
. check if the sock is AF_INET6 before looking into the pinet6
  area that is not present anymore in AF_INET4 struct sock, this
  fixes the bug reported by Carl Ritson on netdev
. replace __constant_hton* with hton*, as both generate the same
  code and __constant_* should be only used when initializing
  static variables