ServiceManager: Implement PING_TRANSACTION

Stop printing "invalid id " to stderr every time a process tries to
connect to the servicemanager.

Change-Id: Ib0e5a0375bfa2dec2c2f9cd668bd5dda46ed6588
diff --git a/cmds/servicemanager/binder.h b/cmds/servicemanager/binder.h
index c207279..7915fc2 100644
--- a/cmds/servicemanager/binder.h
+++ b/cmds/servicemanager/binder.h
@@ -33,6 +33,8 @@
 #define SVC_MGR_NAME "android.os.IServiceManager"
 
 enum {
+    /* Must match definitions in IBinder.h and IServiceManager.h */
+    PING_TRANSACTION  = B_PACK_CHARS('_','P','N','G'),
     SVC_MGR_GET_SERVICE = 1,
     SVC_MGR_CHECK_SERVICE,
     SVC_MGR_ADD_SERVICE,