NetworkAgent: Send primitive integer in score

|Integer| is not parcelable and hences crashes when the binder call
crosses a process boundary. Using a primitive integer should suffice
for sending the value to the server. There are no other usage of
|EVENT_NETWORK_SCORE_CHANGED| in the codebase.

Bug: 112358948
Test: Device boots up and able to make wifi connection.
Change-Id: I4c8fc17f4b803f69a4d882c71a8ce014a194d1ba