The metered status can depend on the DHCP lease, as we accept the ANDROID_METERED vendor option. That means, on a DHCP update we need to re-evaluate the metered flag.
This fixes a potential race, where IPv6 might succeed first and activation completes (with GUESS_NO metered flag). A subsequent DHCPv4 update requires to re-evaluate that decision.
Test: @connection_metered_guess_yes
This is supposed to help with test @connection_metered_guess_yes. See for example here.
Note that it doesn't fully fix the current version of connection_metered_guess_yes, because there is still a race that the metered state is not yet update-to-date the moment we are activated. We would either need to disable IPv6 or wait until IPv4 is ready.