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.
Move the UDP receive probes to the beginning of udp_input().
Use the right var name for the ip header.
Merge branch '20130421-ip-provider' into 20130427-udp-provider
Merge branch '20130427-udp-provider' into 20130428-tcp-provider
Add a flag variable to indicate whether the receive probe fired or not.