Fill out the -p section: add descriptions for all the fields and flags
printed for each prefix.
Merge branch '20130417-rtsold-interfaces' into markj-develop
Move the IP receive probes to the beginning of ip_input() and
ip6_input() rather than waiting until they call up into the higher-level
protocol handlers. So now we just make sure the IP version number and
the header length are sane before firing the probes.
Merge branch '20130421-ip-provider' into markj-develop