OkHttpClientTransportTest's proxy to use localhost

Fixes #8080. The address 0.0.0.0 (that comes from new Socket(0).
.getLocalSocketAddress()) is for listening with a server, but it
is not meant to be used as the destination address as per
"3.2.1.3 Addressing" in RFC 1122

okhttp/src/test/java/io/grpc/okhttp/OkHttpClientTransportTest.java

@@ -1866,7 +1866,8 @@ public void proxy_200() throws Exception {
         INITIAL_WINDOW_SIZE,
         HttpConnectProxiedSocketAddress.newBuilder()
             .setTargetAddress(targetAddress)
-            .setProxyAddress(serverSocket.getLocalSocketAddress()).build(),
+            .setProxyAddress(new InetSocketAddress("localhost", serverSocket.getLocalPort()))
+            .build(),
         tooManyPingsRunnable,
         DEFAULT_MAX_INBOUND_METADATA_SIZE,
         transportTracer,
@@ -1923,7 +1924,8 @@ public void proxy_500() throws Exception {
         INITIAL_WINDOW_SIZE,
         HttpConnectProxiedSocketAddress.newBuilder()
             .setTargetAddress(targetAddress)
-            .setProxyAddress(serverSocket.getLocalSocketAddress()).build(),
+            .setProxyAddress(new InetSocketAddress("localhost", serverSocket.getLocalPort()))
+            .build(),
         tooManyPingsRunnable,
         DEFAULT_MAX_INBOUND_METADATA_SIZE,
         transportTracer,
@@ -1979,7 +1981,8 @@ public void proxy_immediateServerClose() throws Exception {
         INITIAL_WINDOW_SIZE,
         HttpConnectProxiedSocketAddress.newBuilder()
             .setTargetAddress(targetAddress)
-            .setProxyAddress(serverSocket.getLocalSocketAddress()).build(),
+            .setProxyAddress(new InetSocketAddress("localhost", serverSocket.getLocalPort()))
+            .build(),
         tooManyPingsRunnable,
         DEFAULT_MAX_INBOUND_METADATA_SIZE,
         transportTracer,