integration tests should validate packet count

Some of the integration tests (`doTcCheck()`, `doTcxCheck()`, `doXdpCheck()`) aren't testing for a non-zero count. They are just checking for the string "packets received" and "bytes received", whereas their App equivalent (`doAppTcCheck()`, `doAppTcxCheck()`, `doAppXdpCheck()`) make sure a non-zero count is received. Make these tests more like their App equivalent.

Locate the integration-test implementations of doTcCheck(), doTcxCheck(), and doXdpCheck(), then compare them with doAppTcCheck(), doAppTcxCheck(), and doAppXdpCheck(). Update the integration checks so they validate a non-zero packet count, and run the relevant integration tests to confirm they reject zero packets.

Written by the indexing model from the issue text.