netd: BandwidthController: return extra info on gettetherstats failure

Use the error message string to report the raw parsed data in case of
failure.

Bug:5543131
Change-Id: If9f3bcea09fd3ab8a506955d8153b3430bfd239c
diff --git a/BandwidthController.h b/BandwidthController.h
index 861c63e..1aa19e5 100644
--- a/BandwidthController.h
+++ b/BandwidthController.h
@@ -75,7 +75,7 @@
      * stats should have ifaceIn and ifaceOut initialized.
      * Byte counts should be left to the default (-1).
      */
-    int getTetherStats(TetherStats &stats);
+    int getTetherStats(TetherStats &stats, std::string &extraProcessingInfo);
 
 protected:
     class QuotaInfo {
@@ -122,8 +122,10 @@
     /*
      * stats should have ifaceIn and ifaceOut initialized.
      * fp should be a file to the FORWARD rules of iptables.
+     * extraProcessingInfo: contains raw parsed data, and error info.
      */
-    static int parseForwardChainStats(TetherStats &stats, FILE *fp);
+    static int parseForwardChainStats(TetherStats &stats, FILE *fp,
+				      std::string &extraProcessingInfo);
 
     /*------------------*/