refactor(dnsx): prepare for merging with netxlite (#515)

Part of https://github.com/ooni/probe/issues/1591

internal/netxlite/dnsx/mocks/dnstransport.go

@@ -0,0 +1,41 @@
+package mocks
+
+import "context"
+
+// DNSTransport allows mocking dnsx.DNSTransport.
+type DNSTransport struct {
+	MockRoundTrip func(ctx context.Context, query []byte) (reply []byte, err error)
+
+	MockRequiresPadding func() bool
+
+	MockNetwork func() string
+
+	MockAddress func() string
+
+	MockCloseIdleConnections func()
+}
+
+// RoundTrip calls MockRoundTrip.
+func (txp *DNSTransport) RoundTrip(ctx context.Context, query []byte) (reply []byte, err error) {
+	return txp.MockRoundTrip(ctx, query)
+}
+
+// RequiresPadding calls MockRequiresPadding.
+func (txp *DNSTransport) RequiresPadding() bool {
+	return txp.MockRequiresPadding()
+}
+
+// Network calls MockNetwork.
+func (txp *DNSTransport) Network() string {
+	return txp.MockNetwork()
+}
+
+// Address calls MockAddress.
+func (txp *DNSTransport) Address() string {
+	return txp.MockAddress()
+}
+
+// CloseIdleConnections calls MockCloseIdleConnections.
+func (txp *DNSTransport) CloseIdleConnections() {
+	txp.MockCloseIdleConnections()
+}