Fix "malformed_packet" errors
Fix "malformed_packet" errors

As reported in https://github.com/insomniacslk/dublin-traceroute/issues/27 .
The code that parses the packet responses does not check if the inner IP
and UDP layers are present in the response ICMP, but blindly assumed so.
This commit fixes this behaviour.

insomniacslk/dublin-traceroute,insomniacslk/dublin-traceroute,insomniacslk/dublin-traceroute,insomniacslk/dublin-traceroute,insomniacslk/dublin-traceroute