shill: Log DBus address of dhcpcd on creation

Log the unique DBus identifier of dhcpcd when we create proxies.  This
will help us debug crashes where the proxy fails to find dhcpcd at a
particular DBus identifier.

BUG=chromium-os:15958
TEST=Run shill, see log messages with the right information when we
start configuring L3.

Change-Id: I58ae8c866753c5b91fb922eb9cda8d8b95effb85
Reviewed-on: https://gerrit.chromium.org/gerrit/38228
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Christopher Wiley <wiley@chromium.org>
Tested-by: Christopher Wiley <wiley@chromium.org>
diff --git a/dhcp_config.cc b/dhcp_config.cc
index 3044c86..cac18f4 100644
--- a/dhcp_config.cc
+++ b/dhcp_config.cc
@@ -137,7 +137,7 @@
 
 void DHCPConfig::InitProxy(const string &service) {
   if (!proxy_.get()) {
-    SLOG(DHCP, 2) << "Init DHCP Proxy: " << device_name() << " at " << service;
+    LOG(INFO) << "Init DHCP Proxy: " << device_name() << " at " << service;
     proxy_.reset(proxy_factory_->CreateDHCPProxy(service));
   }
 }