Add cellular null cipher transparency system APIs

This commit adds two new system APIs to support celluar null cipher
transparency. These APIs will allow setting and getting whether
the notifications should be sent when the modem switches to / from
a null cipher.

Bug: 316592273
Test: atest TelephonyManagerTest
Change-Id: I38e0bd069e60ff245ba7ab645c073a1aeca83fd2
3 files changed