IPV6 - Attempt to fix tcp46 compatibility listen sockets

IPV6 - Attempt to fix tcp46 compatibility listen sockets

* When creating the accepted socket via the syncache, if the
  listen socket is INET6 but allows compatibility connections
  the inp created via sonewconn() will probably set IN6P_IPV6_V6ONLY.

  This flag must be cleared if the incoming connection is
  actually IPV4, otherwise tcp6_soport() will not properly
  fall through to tcp_soport().

* NOTE: Even though the connection is IPV4 the socket's protocol
  is copied from the listen socket which is INET6.  This seems
  to work ok but it isn't ideal.

* When connecting make sure that IPV6 connections use cpu 0 for
  now (we don't have a proper hash for IPV6 addresses yet).

Reported-by: corecode