shill: Makes netlink message logging finer-grained.

Logs netlink message headers at a more permissive log level than the
bodies of those messages.

While I was in there, I changed a couple comments.

BUG=None
TEST=unittest.

Change-Id: I7d6e415dd5a7d3ec86e260a0a6664b8be813f42a
Reviewed-on: https://gerrit.chromium.org/gerrit/48015
Reviewed-by: Wade Guthrie <wdg@chromium.org>
Tested-by: Wade Guthrie <wdg@chromium.org>
Commit-Queue: Wade Guthrie <wdg@chromium.org>
diff --git a/callback80211_metrics.cc b/callback80211_metrics.cc
index 28437ad..511609c 100644
--- a/callback80211_metrics.cc
+++ b/callback80211_metrics.cc
@@ -37,10 +37,9 @@
   const Nl80211Message &message =
       * reinterpret_cast<const Nl80211Message *>(&netlink_message);
 
-  SLOG(WiFi, 3) << "Received " << message.command_string()
-                << " (" << + message.command() << ")";
   if (metrics_ &&
       message.command() == DeauthenticateMessage::kCommand) {
+    SLOG(WiFi, 3) << "Handling Deauthenticate Message";
     Metrics::WiFiDisconnectByWhom by_whom =
         message.const_attributes()->IsFlagAttributeTrue(
             NL80211_ATTR_DISCONNECTED_BY_AP) ?