Don't care about the Linux kernel version number.

What OS-specific and OS-version-specific features tcpdump uses
*directly* should be checked for specifically; if it *requires* features
not available with systems using a 1.x kernel, the configure should fail
because of *that*, and if it doesn't require any such features, we
should allow building on/for systems with a 1.x kernel.

If there are issues with *libpcap* on systems with a 1.x kernel, then
that should be handled in the libpcap configure script - and, even if
it's impossible to capture traffic on such a system, you can build a
version of libpcap that can read files but not capture, which would give
you a tcpdump that could, at least, read files from other machines.
BGP assumes octets, not bytes; no need to use NBBY, just use 8.

Everywhere else in the BGP dissector, we just use a constant 8 for the
number of bits per octet; get rid of the one place where we use NBBY.

This gets rid of the one and only place we use NBBY; get rid of our own
definition of it.
Clean up protocol ID printing.

If getprotobynumber() doesn't return a valid protocol name, just print
the protocol number.

Don't bother with setprotoent() and endprotoent() - none of the other
dissectors using getprotobynumber() use them and, if it's a useful
optimization, we should do the optimization in a common routine for all
callers (or do some other optimization, e.g. reading the entire protocol
list and building a table in which we can do a quick lookup).
Update to autoconf 2.69.