Catch creation of NetworkRequest without NetCap

Using reflection you could do this and it would crash the system.
Thanks, ServiceFuzzer!

bug:17379629
Change-Id: I8b470bda78a69761ccd92496746f5d295b5d07f2

core/java/android/net/NetworkRequest.java

@@ -52,6 +52,9 @@ public class NetworkRequest implements Parcelable {
      * @hide
      */
     public NetworkRequest(NetworkCapabilities nc, int legacyType, int rId) {
+        if (nc == null) {
+            throw new NullPointerException();
+        }
         requestId = rId;
         networkCapabilities = nc;
         this.legacyType = legacyType;