At a point not too far in the future, we will be switching from the
hardcoded MINIX3 implementation of the getifaddrs(3) libc routine to
the proper NetBSD implementation. The latter uses the
net.route.rtable sysctl functionality to obtain its information. In
order make the transition as painless as possible, this patch adds
basic support for that net.route.rtable functionality to INET and
LWIP, using the remote MIB (RMIB) facility.