Add setFirewallChainEnabled API

To deprecated firewallEnableChildChain netd binder and move the
functionality to tethering (connectivity) mainline module, expose
setFirewallChainEnabled to support the caller outside the module.
Currently the API are still call to netd. Will replace with the
implementation inside tethering (connectivity) module.

Bug: 209935649
Test: atest CtsHostsideNetworkTests
Change-Id: I9b64c9d12260521489a87fbeae5afbee2a8ea8f6
4 files changed