Fix NPE in tethering startup

mUserManager should be ready before #makeTethering because mTethering may
call isTetheringSupported which need to reference mUserManager

Bug: 148642028
Test: build
Change-Id: I100b5d6cc8f49640c33fa930b819033de5d6492c
diff --git a/Tethering/src/com/android/server/connectivity/tethering/TetheringService.java b/Tethering/src/com/android/server/connectivity/tethering/TetheringService.java
index 7dc5c5f..020b32a 100644
--- a/Tethering/src/com/android/server/connectivity/tethering/TetheringService.java
+++ b/Tethering/src/com/android/server/connectivity/tethering/TetheringService.java
@@ -77,8 +77,8 @@
         mLog.mark("onCreate");
         mDeps = getTetheringDependencies();
         mContext = mDeps.getContext();
-        mTethering = makeTethering(mDeps);
         mUserManager = (UserManager) mContext.getSystemService(Context.USER_SERVICE);
+        mTethering = makeTethering(mDeps);
     }
 
     /**