Add the new RIL requests to start/stop network scan

The CL defines the RIL API including the methods and structs which will
be used start and stop the network scan.

Test: Telephony Sanity Test
Bug: 30954762

Change-Id: I18462bf4aa5e8a9497d5eb214d905e4e7c827a04
(cherry picked from commit b187e9f9)