Add mDNS device discovery for adb client

Test: Was able to discover a raspberry pi.
Bug: 28074466
(cherry picked from e292cd16760321fccc99c8c261cb92fa4b6462ab)

Change-Id: Id9571576457a4a0a078e48a274a4e8eac78bfe2b
diff --git a/adb/client/main.cpp b/adb/client/main.cpp
index 97a54fd..606203c 100644
--- a/adb/client/main.cpp
+++ b/adb/client/main.cpp
@@ -117,6 +117,8 @@
 
     init_transport_registration();
 
+    init_mdns_transport_discovery();
+
     usb_init();
     local_init(DEFAULT_ADB_LOCAL_TRANSPORT_PORT);