test: improve message in net-connect-local-error

test-net-connect-local-error can fail with messages that report
`AssertionError: undefined === 12346`. Unfortunately, this doesn't
provide sufficient information to identify what went wrong with the
test. Increase information provided.

test/parallel/test-net-connect-local-error.js

@@ -10,6 +10,14 @@ const client = net.connect({
 });
 
 client.on('error', common.mustCall(function onError(err) {
-  assert.strictEqual(err.localPort, common.PORT);
-  assert.strictEqual(err.localAddress, common.localhostIPv4);
+  assert.strictEqual(
+    err.localPort,
+    common.PORT,
+    `${err.localPort} !== ${common.PORT} in ${err}`
+  );
+  assert.strictEqual(
+    err.localAddress,
+    common.localhostIPv4,
+    `${err.localAddress} !== ${common.localhostIPv4} in ${err}`
+  );
 }));