I was running the p4c tests on an Ubuntu 20.04 system today. Last week when I tried this, Scapy 2.4.x was the version installed, but today it was Scapy 2.5.0, which seems like it may have removed the method convert_to. Whatever the reason, attempting to call convert_to(Raw) on many packets in STF tests was causing an exception to be thrown. The tests pass with the proposed changes in this PR, and I believe should work fine with older versions of Scapy on Python3, too.