Start retiring socket_loopback_client.

Bug: http://b/31537253
Test: can still talk to adb
Change-Id: Icfd7f00d35cf963befc139e81904790b4b8b67c0
diff --git a/adb/sysdeps.h b/adb/sysdeps.h
index 3ed589c..ded8214 100644
--- a/adb/sysdeps.h
+++ b/adb/sysdeps.h
@@ -594,7 +594,7 @@
 }
 
 inline int network_loopback_client(int port, int type, std::string* error) {
-  return _fd_set_error_str(socket_loopback_client(port, type), error);
+  return _fd_set_error_str(socket_network_client("localhost", port, type), error);
 }
 
 inline int network_loopback_server(int port, int type, std::string* error) {