Refactor Parasitictraceroute.

In particular, scapy.supersocket.L3RawSocket does not capture
transmitted packets.
Fix bug that lead to the transport name not being correct when the pluggable transport was not installed.

Thanks to asn for spotting it.
Merge pull request #348 from TheTorProject/fix/parasitictraceroute

Refactor Parasitictraceroute.