Separate system default network from Ike Session network

- Keep the most recent copy of the IWLAN provided system default
  network, and update the IKE session's network only when required
  conditions are met.

Test: On-device Smart DSDA regression tests to ensure IWLAN tunnel setup
works smoothly on switching default network.
Bug: 249854222

Change-Id: I85e86beb538f09f06404da9cb0c596be393a618f
2 files changed