adb: fix register_socket_transport related double-closes.

Multiple codepaths were closing the fd they passed into
register_socket_transport on failure, which would close the fd itself.

Switch things over to unique_fd to make it clear that we don't actually
have to close on failure.

Test: mma
Change-Id: I2d9bdcb1142c24931d970f99ebdf9a8051daf05c
diff --git a/adb/adb.h b/adb/adb.h
index 7e9af9e..26b5fa1 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -133,7 +133,7 @@
 int adb_server_main(int is_daemon, const std::string& socket_spec, int ack_reply_fd);
 
 /* initialize a transport object's func pointers and state */
-int init_socket_transport(atransport* t, int s, int port, int local);
+int init_socket_transport(atransport* t, unique_fd s, int port, int local);
 void init_usb_transport(atransport* t, usb_handle* usb);
 
 std::string getEmulatorSerialString(int console_port);