shill: Puts netlink message CreateAttribute calls in msg constructor.

This doesn't move Create*Attribute calls from nested attributes (because
at least some of those have to be created on site -- arrays on nested
attributes, for instance) nor from unittests that create messages that
normally come from the kernel.

BUG=chromium:240446
TEST=unittest

Change-Id: I192a452ec229d0a0ea2b314ad0cb56bff295e339
Reviewed-on: https://gerrit.chromium.org/gerrit/56815
Reviewed-by: Wade Guthrie <wdg@chromium.org>
Tested-by: Wade Guthrie <wdg@chromium.org>
Commit-Queue: Wade Guthrie <wdg@chromium.org>
diff --git a/nl80211_message.cc b/nl80211_message.cc
index 5b142c3..ee43e11 100644
--- a/nl80211_message.cc
+++ b/nl80211_message.cc
@@ -619,7 +619,7 @@
 const char TriggerScanMessage::kCommandString[] = "NL80211_CMD_TRIGGER_SCAN";
 
 TriggerScanMessage::TriggerScanMessage()
-  : Nl80211Message(kCommand, kCommandString) {
+    : Nl80211Message(kCommand, kCommandString) {
   attributes()->CreateAttribute(
       NL80211_ATTR_IFINDEX, Bind(&NetlinkAttribute::NewNl80211AttributeFromId));
   attributes()->CreateAttribute(