add union field that is used in the kernel for SIT/GRE tunneling ICMPv4 messages. see linux commit 20e1954fe238dbe5f8d3a979e593fe352bd703cf
@@ -23,6 +23,7 @@ struct icmphdr {
uint16_t __unused;
uint16_t mtu;
} frag;
+ uint8_t reserved[4];
} un;
};