* SECURITY: Correctly set "unused" ICMP header field.
* Do not send ICMP errors in response to unknown incoming ICMP.
* SECURITY: Fix IP length check not to crash on very short packets.
* SECURITY: Correctly set "unused" ICMP header field.
* Do not send ICMP errors in response to unknown incoming ICMP.
* SECURITY: Fix IP length check not to crash on very short packets.