We still need u_intN_t.

We still need u_intN_t.

Some libpcap headers use them, and even if we change libpcap to use
uintN_t, we don't require that tcpdump 4.x go with libpcap 1.x - we
allow people to install the latest tcpdump even if they have an older
libpcap and don't want to install a newer one.

However, we now define them in terms of the C99 uintN_t types, rather
than trying to guess what's appropriate; using unsigned long long for
u_int64_t meant that, on some platforms, u_int64_t didn't match
PRI[doux]64, and using unsigned long obviously won't work on ILP32
platforms.

Also, we already had calls to the autoconf macros for C99 types; get rid
of the ones we added.

Also also, clean up a comment in tcpdump-stdinc.h.