shill: Add C++11 override specifier to destructors of derived classes.

BUG=None
TEST=`USE=wimax FEATURES=test emerge-$BOARD platform2`

Change-Id: I88d4e29165869b26924cccb94ac940dc8961c312
Reviewed-on: https://chromium-review.googlesource.com/212267
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
diff --git a/nl80211_message.h b/nl80211_message.h
index 7c907cc..e5f952e 100644
--- a/nl80211_message.h
+++ b/nl80211_message.h
@@ -26,7 +26,7 @@
 
   Nl80211Message(uint8_t command, const char *command_string)
       : GenericNetlinkMessage(nl80211_message_type_, command, command_string) {}
-  virtual ~Nl80211Message() {}
+  ~Nl80211Message() override {}
 
   // Gets the family_id / message_type for all Nl80211 messages.
   static uint16_t GetMessageType();