Merge "Replace subnet mask calculation to Inet4AddressUtils" into sc-dev

import androidx.preference.PreferenceFragmentCompat;

import androidx.preference.PreferenceScreen;

import com.android.net.module.util.NetUtils;

import com.android.net.module.util.Inet4AddressUtils;

import com.android.settings.R;

import com.android.settings.Utils;

import com.android.settings.core.FeatureFlags;

import java.net.Inet4Address;

import java.net.Inet6Address;

import java.net.InetAddress;

import java.net.UnknownHostException;

import java.time.Duration;

import java.time.Instant;

import java.time.ZonedDateTime;

    private static String ipv4PrefixLengthToSubnetMask(int prefixLength) {

        try {

            InetAddress all = InetAddress.getByAddress(

                    new byte[]{(byte) 255, (byte) 255, (byte) 255, (byte) 255});

            return NetUtils.getNetworkPart(all, prefixLength).getHostAddress();

        } catch (UnknownHostException e) {

            return Inet4AddressUtils.getPrefixMaskAsInet4Address(prefixLength).getHostAddress();

        } catch (IllegalArgumentException e) {

            return null;

        }

    }