rename it again to DLT_PPP_PPPD, and rename other #defines to match.
Add backwards-compatibility #defines of DLT_PPP_WITH_DIRECTION and
DLT_LINUX_PPP_WITHDIRECTION for software that used them.
the first byte (0xff) of the PPP header (0xff03) is tweaked to accomodate
the direction 0x00 = IN, 0x01 = OUT
the DLT_ supports the libpcap tokens "inbound" and "outbound"
./configure --enable-ipv6 (requires getaddrinfo(3) and getnameinfo(3)).
TODO: make it work even without getaddrinfo(3) or getnameinfo(3)
(or, tcpdump/configure.in should provide alternative version by
AC_REPLACE_FUNCS)
TODO: make IPv6 filtering code work by default
TODO: make "protochain" friendly with optimization