e2e: improve p2p mode selection (#6929)

The previous implemention of hybrid set testing, which was entirely my
own creation, was a bit peculiar, and I think this probably clears thins up.

The previous implementation had far fewer legacy nodes in hybrid
networks, *and* also for some reason that I can't quite explain,
caused a test case to fail.

test/e2e/pkg/testnet.go

@@ -182,7 +182,7 @@ func LoadTestnet(file string) (*Testnet, error) {
 			Perturbations:    []Perturbation{},
 			LogLevel:         manifest.LogLevel,
 			QueueType:        manifest.QueueType,
-			UseLegacyP2P:     manifest.UseLegacyP2P && nodeManifest.UseLegacyP2P,
+			UseLegacyP2P:     nodeManifest.UseLegacyP2P,
 		}
 
 		if node.StartAt == testnet.InitialHeight {