DataCallSessionStats captures Cross-SIM calling

- DataCallSessionStats monitors the system default network's transport
  to determine when a PDN is established on IWLAN, whether it is WiFi
  Calling or Backup Calling.

Bug: 294240210
Test: New file DataCallSessionStatsTest. Live test.
Change-Id: Idfd755f5b7f5f6167e94f934e1fc12f9608be8a9