Add some truncation checks.

Add some truncation checks.
#include <netdb.h> for MAXHOSTNAMELEN on Solaris
Use EXTRACT_16BITS to extract 16-bit quantities
Print withdrawn routes if we think we can
Print must-be-zero attribute flags if they're not zero

Partly from: Jim Vaughn, http://www.tcpdump.org/lists/patches/107