cmd/devp2p: implement snap protocol testing (#24276)

This also contains some changes to the protocol handler to
make the tests pass.

cmd/devp2p/internal/ethtest/suite_test.go

@@ -55,6 +55,27 @@ func TestEthSuite(t *testing.T) {
 	}
 }
 
+func TestSnapSuite(t *testing.T) {
+	geth, err := runGeth()
+	if err != nil {
+		t.Fatalf("could not run geth: %v", err)
+	}
+	defer geth.Close()
+
+	suite, err := NewSuite(geth.Server().Self(), fullchainFile, genesisFile)
+	if err != nil {
+		t.Fatalf("could not create new test suite: %v", err)
+	}
+	for _, test := range suite.SnapTests() {
+		t.Run(test.Name, func(t *testing.T) {
+			result := utesting.RunTAP([]utesting.Test{{Name: test.Name, Fn: test.Fn}}, os.Stdout)
+			if result[0].Failed {
+				t.Fatal()
+			}
+		})
+	}
+}
+
 // runGeth creates and starts a geth node
 func runGeth() (*node.Node, error) {
 	stack, err := node.New(&node.Config{