Add keepAlive message type in send request API for satellite service

Bug: 327032155
Test: atest DatagramControllerTest DatagramDispatcherTest PointingAppControllerTest
SatelliteManagerTestOnMockService
SMS/MMS/Call with live network

Change-Id: I7576171b92e4d1436605209334cbc54a3d4bc1b3
3 files changed