[Thread] use toHexString for toString()

dumpHexString will create additional representations other than a HEX string, it's suitable for raw logging message but not in a Object#toString.

Change-Id: I184eb10bafa2db1103a4ef5cf82250db52aec278
diff --git a/thread/framework/java/android/net/thread/ActiveOperationalDataset.java b/thread/framework/java/android/net/thread/ActiveOperationalDataset.java
index 4a7d3a7..22457f5 100644
--- a/thread/framework/java/android/net/thread/ActiveOperationalDataset.java
+++ b/thread/framework/java/android/net/thread/ActiveOperationalDataset.java
@@ -18,7 +18,7 @@
 
 import static com.android.internal.util.Preconditions.checkArgument;
 import static com.android.internal.util.Preconditions.checkState;
-import static com.android.net.module.util.HexDump.dumpHexString;
+import static com.android.net.module.util.HexDump.toHexString;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static java.util.Objects.requireNonNull;
@@ -610,7 +610,7 @@
         sb.append("{networkName=")
                 .append(getNetworkName())
                 .append(", extendedPanId=")
-                .append(dumpHexString(getExtendedPanId()))
+                .append(toHexString(getExtendedPanId()))
                 .append(", panId=")
                 .append(getPanId())
                 .append(", channel=")
@@ -1109,7 +1109,7 @@
             sb.append("{rotation=")
                     .append(mRotationTimeHours)
                     .append(", flags=")
-                    .append(dumpHexString(mFlags))
+                    .append(toHexString(mFlags))
                     .append("}");
             return sb.toString();
         }