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/transport.h b/adb/transport.h
index 490e513..4d97fc7 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -187,6 +187,7 @@
 void update_transports(void);
 
 void init_transport_registration(void);
+void init_mdns_transport_discovery(void);
 std::string list_transports(bool long_listing);
 atransport* find_transport(const char* serial);
 void kick_all_tcp_devices();
@@ -194,6 +195,9 @@
 void register_usb_transport(usb_handle* h, const char* serial,
                             const char* devpath, unsigned writeable);
 
+/* Connect to a network address and register it as a device */
+void connect_device(const std::string& address, std::string* response);
+
 /* cause new transports to be init'd and added to the list */
 int register_socket_transport(int s, const char* serial, int port, int local);