Update toString() to use the correct request

Update ConnectivityService.NetworkReassignment#toString to use either
the current satisfier's request otherwise highest priority request when
executing toString(). This is part of the mulilayered request changes.

Bug: 173336774
Bug: 171991028
Test: atest FrameworksNetTests
Change-Id: Ibed6cdd4522133164b2b919f62ecc9411943f026

services/core/java/com/android/server/ConnectivityService.java

@@ -6814,7 +6814,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
             }
 
             public String toString() {
-                return mRequest.request.requestId + " : "
+                return mRequest.mRequests.get(0).requestId + " : "
                         + (null != mOldNetwork ? mOldNetwork.network.netId : "null")
                         + " → " + (null != mNewNetwork ? mNewNetwork.network.netId : "null");
             }