shill: Make nl80211 broadcast callback a list of callbacks.

This will allow multiple callbacks to be called when an nl80211 message
is received.  This allows a user to add a callback without displacing
others (e.g. disconnect metrics).

BUG=chromium-os:35468
TEST=unit tests, manual tests

Change-Id: I19d6cfac5754ea1d2a699de80d4465c49fec888c
Reviewed-on: https://gerrit.chromium.org/gerrit/36061
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Wade Guthrie <wdg@google.com>
Tested-by: Wade Guthrie <wdg@google.com>
diff --git a/shill_daemon.h b/shill_daemon.h
index 9232c2a..8f2df30 100644
--- a/shill_daemon.h
+++ b/shill_daemon.h
@@ -14,6 +14,7 @@
 #include "shill/manager.h"
 #include "shill/metrics.h"
 #include "shill/sockets.h"
+#include "shill/callback80211_object.h"
 #include "shill/callback80211_metrics.h"
 
 namespace shill {
@@ -63,6 +64,7 @@
   DHCPProvider *dhcp_provider_;
   Config80211 *config80211_;
   scoped_ptr<Manager> manager_;
+  Callback80211Object callback80211_output_;
   Callback80211Metrics callback80211_metrics_;
   EventDispatcher dispatcher_;
   Sockets sockets_;