Use more specific sockaddr type for inpcb notify.

Use more specific sockaddr type for inpcb notify.

in_pcbnotifyall() is an IPv4 only function.  All callers check that
sockaddr dst is in fact a sockaddr_in.  Pass the more spcific type
and remove the runtime check at beginning of in_pcbnotifyall().
Use const sockaddr_in in in_pcbnotifyall() and const sockaddr_in6
in6_pcbnotify() as dst parameter.

OK millert@