Check iface by TextUtils.equals

In current equals method, if iface is null then it will cause
null object reference when checking iface.
Thus, use TextUtils.equals to check iface so that it can compare
null iface.

Bug: 210073043
Test: FrameworksNetTests, NetworkStaticLibTests
Change-Id: I2bd8127cb030ea54438382ee89961590fffbc31a

framework-t/src/android/net/NetworkStats.java

@@ -28,6 +28,7 @@ import android.os.Parcel;
 import android.os.Parcelable;
 import android.os.Process;
 import android.os.SystemClock;
+import android.text.TextUtils;
 import android.util.SparseBooleanArray;
 
 import com.android.internal.annotations.VisibleForTesting;
@@ -410,7 +411,7 @@ public final class NetworkStats implements Parcelable {
                         && roaming == e.roaming && defaultNetwork == e.defaultNetwork
                         && rxBytes == e.rxBytes && rxPackets == e.rxPackets
                         && txBytes == e.txBytes && txPackets == e.txPackets
-                        && operations == e.operations && iface.equals(e.iface);
+                        && operations == e.operations && TextUtils.equals(iface, e.iface);
             }
             return false;
         }