don't rely on AF_MAX (comes from kernel include): check for nil explicitly,

don't rely on AF_MAX (comes from kernel include): check for nil explicitly,
use our own idea of table size.  Use syslog to (optionally) log bad packets.
Don't respond to routing inquiries from a router unless we are suppliers
(really want to respondto everything but broadcasts, but haven't got
the "to" address.)

SCCS-vsn: sbin/routed/af.c 5.3
SCCS-vsn: sbin/routed/af.h 5.2
SCCS-vsn: sbin/routed/if.c 5.2
SCCS-vsn: sbin/routed/input.c 5.2
SCCS-vsn: sbin/routed/main.c 5.6
SCCS-vsn: sbin/routed/tables.c 5.2