Include port info in HTTP headers for Netty client

This commit adds the port information in the "Host" HTTP request header
for the Netty-based HTTP client.

Issue: SPR-15706

spring-web/src/main/java/org/springframework/http/client/Netty4ClientHttpRequest.java

@@ -142,7 +142,7 @@ class Netty4ClientHttpRequest extends AbstractAsyncClientHttpRequest implements
 		FullHttpRequest nettyRequest = new DefaultFullHttpRequest(
 				HttpVersion.HTTP_1_1, nettyMethod, path, this.body.buffer());
 
-		nettyRequest.headers().set(HttpHeaders.HOST, this.uri.getHost());
+		nettyRequest.headers().set(HttpHeaders.HOST, this.uri.getHost() + ":" + getPort(uri));
 		nettyRequest.headers().set(HttpHeaders.CONNECTION, "close");
 		for (Map.Entry<String, List<String>> entry : headers.entrySet()) {
 			nettyRequest.headers().add(entry.getKey(), entry.getValue());

spring-web/src/test/java/org/springframework/http/client/AbstractMockWebServerTestCase.java

@@ -48,6 +48,8 @@ public class AbstractMockWebServerTestCase {
 		public MockResponse dispatch(RecordedRequest request) throws InterruptedException {
 			try {
 				if (request.getPath().equals("/echo")) {
+					assertThat(request.getHeader("Host"),
+							Matchers.containsString("localhost:" + port));
 					MockResponse response = new MockResponse()
 							.setHeaders(request.getHeaders())
 							.setHeader("Content-Length", request.getBody().size())