Network Traffic: Consider CLAT interfaces (IPv6)

IPv6-only networks that support 464XLAT use CLAT to access IPv4
addresses, but the traffic that occurs over the CLAT interface is
tracked separately; it is not reflected at all in the stats of the
underlying interface, so prior to this change, IPv4 traffic on
applicable IPv6-only networks is not reflected in the network traffic
monitor, either.

While there is no exposed API to retrieve stacked interfaces, we can
still try to grab the stats for a CLAT interface (which always starts
with "v4-"), just in case it exists, and if so, add in those stats.

Test: Manual: While connected to an IPv6-only network, such as a
T-Mobile cellular data connection, attempt to load https://1.1.1.1
in a browser while the network traffic monitor is enabled. Reload
the page / choose different languages to cause traffic to occur,
and it should be reflected in the traffic monitor.

Issue: calyxos#792
Co-authored-by: Oliver Scott <olivercscott@gmail.com>
Change-Id: Ida768ebe73a47bb06da53aeb7b5c6882f0090e75

sdk/src/java/org/lineageos/internal/statusbar/NetworkTraffic.java

@@ -47,12 +47,16 @@
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.stream.Stream;
 
 public class NetworkTraffic extends TextView {
     private static final String TAG = "NetworkTraffic";
 
     private static final boolean DEBUG = false;
 
+    // This must match the interface prefix in Connectivity's clatd.c.
+    private static final String CLAT_PREFIX = "v4-";
+
     private static final int MODE_DISABLED = 0;
     private static final int MODE_UPSTREAM_ONLY = 1;
     private static final int MODE_DOWNSTREAM_ONLY = 2;
@@ -163,12 +167,13 @@ private void recalculateStats() {
                 // Sum tx and rx bytes from all sources of interest
                 long txBytes = 0;
                 long rxBytes = 0;
-                // Add interface stats
-                for (LinkProperties linkProperties : mLinkPropertiesMap.values()) {
-                    final String iface = linkProperties.getInterfaceName();
-                    if (iface == null) {
-                        continue;
-                    }
+                // Add interface stats, including stats from Clat's IPv4 interface
+                // (for applicable IPv6 networks). Stats are 0 if it doesn't exist.
+                final String[] ifaces = mLinkPropertiesMap.values().stream()
+                        .map(link -> link.getInterfaceName()).filter(iface -> iface != null)
+                        .flatMap(iface -> Stream.of(iface, CLAT_PREFIX + iface))
+                        .toArray(String[]::new);
+                for (String iface : ifaces) {
                     final long ifaceTxBytes = TrafficStats.getTxBytes(iface);
                     final long ifaceRxBytes = TrafficStats.getRxBytes(iface);
                     if (DEBUG) {