Extension API: Replace NetworkScore object with integer in API surface

NetworkScore object is removed as part of punting the network selection refoundation feature out of Android 11.

Test: atest android.net.wifi
Bug: 135573686, 122133502, 136312816, 135572156

Change-Id: Ib4226a4d66ab29fc4b31226d5ece8ad14a14d1e1
Signed-off-by: Mingguang Xu <mingguangxu@google.com>
(cherry picked from commit 705d110d)