This PR adds 'Protocol' field to virtualservice-pod edge metadata.
The relevant tests, TestIstioVirtualServicePodScenario and TestBookInfoScenario, have been extended, such that now they check this property (the amount of traffic routed to each pod by the virtualservice, which was added to the edge metadata in a previous PR, is now being checked as well).
该提问来源于开源项目：skydive-project/skydive
