expose (but still hide) sms user data headers

addresses bug http://b/issue?id=1751571

telephony/java/android/telephony/SmsMessage.java

@@ -517,9 +517,14 @@ public class SmsMessage {
         return mWrappedSmsMessage.getUserData();
     }
 
-    /* Not part of the SDK interface and only needed by specific classes:
-       protected SmsHeader getUserDataHeader()
-    */
+    /**
+     * Return the user data header (UDH).
+     *
+     * @hide
+     */
+    public SmsHeader getUserDataHeader() {
+        return mWrappedSmsMessage.getUserDataHeader();
+    }
 
     /**
      * Returns the raw PDU for the message.

telephony/java/com/android/internal/telephony/gsm/SmsMessage.java

@@ -637,8 +637,6 @@ public class SmsMessage extends SmsMessageBase{
         /**
          * Returns an object representing the user data headers
          *
-         * @return an object representing the user data headers
-         *
          * {@hide}
          */
         SmsHeader getUserDataHeader() {