Refactory the feature flag for ra lifetime filtering

* Make the change default flagged off by using isFeatureEnabled instead
  of isFeatureNotChickenedOut.
* Read the flag on boot (in IpClient constructor, at the same time as
  the config value) instead.
* Make sure only call setIpv6Sysctl when the mUseNewApfFilter and
  mEnableIpClientIgnoreLowRaLifetime are both true.

Bug: 308737632
Test: TH
Change-Id: Ie221fba59a82fb9ce04bf67774ae1014ef3861d0
3 files changed