shill: enable (don't disable) -Wunused

having fixed an unused parameter in the dbus-c++ headers, those
headers no longer have unused parameters. so, if we fix up unused
parameters in shill code, we can compile with -Wunused. (this is
implied by -Wall, as long as we don't override with -Wno-unused.)

BUG=chromium-os:20779
TEST=unittests

- comment out unused parameters in function definitions
- remove some unused local variables
- also: fix an old-style cast

Change-Id: Ie654a7b34d622cecb0f26bd47c17813fe8423001
Reviewed-on: http://gerrit.chromium.org/gerrit/8365
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
diff --git a/rtnl_message_unittest.cc b/rtnl_message_unittest.cc
index 1657bb1..1f8d55f 100644
--- a/rtnl_message_unittest.cc
+++ b/rtnl_message_unittest.cc
@@ -417,7 +417,7 @@
   }
 
   void TestParseRoute(const ByteString &packet,
-                      RTNLMessage::Mode mode,
+                      RTNLMessage::Mode /*mode*/,
                       IPAddress::Family family,
                       int interface_index,
                       const IPAddress &dst,