Don't import stuff from WinPcap that it really shouldn't be exporting.
Define HAVE_U_INT{N}_T,to suppress definition of intN_t in bittypes.h, as
included by <pcap/pcap.h> on Windows.
Define HAVE_OS_IPV6_SUPPORT if AF_INET6 is defined, so that if we're
building with a VC+SDK combination that defines it and struct in6_addr,
we don't define them ourselves.
Have our own routines to convert between IPv4/IPv6 addresses and
strings; that helps if, for example, we want to build binary versions of
tcpdump for Windows that can run both on NT 5 (W2K/WXP), which doesn't
have inet_ntop() or inet_pton(), and NT 6 (Vista/7/8/10), which do. It
also means that we don't require IPv6 library support on UN*X to print
addresses (if somebody wants to build tcpdump for older UN*Xes lacking
IPv6 support in the system library or in add-on libraries).
Get rid of files in the missing directory that we don't need, and
various no-longer-necessary autoconf tests.
