shill: Add a mockable layer for socket.h.

Mock the layer in device_info_unittest.cc. Some cleanup.

BUG=chromium-os:17394
TEST=unit tests

Change-Id: I2ddcb2fd0e01418a463596bf4e3a804b3e3023b2
Reviewed-on: http://gerrit.chromium.org/gerrit/3807
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/device_info.cc b/device_info.cc
index 0172e81..4540f6b 100644
--- a/device_info.cc
+++ b/device_info.cc
@@ -121,7 +121,6 @@
   struct ifinfomsg *msg = reinterpret_cast<struct ifinfomsg *>(NLMSG_DATA(hdr));
   base::hash_map<int, DeviceRefPtr>::iterator ndev =
       devices_.find(msg->ifi_index);
-  int bytes = IFLA_PAYLOAD(hdr);
   int dev_index = msg->ifi_index;
   struct rtattr *rta;
   int rta_bytes;
@@ -146,8 +145,9 @@
 
     VLOG(2) << "add link index "  << dev_index << " name " << link_name;
 
-    if (link_name != NULL)
+    if (link_name) {
       technology = GetDeviceTechnology(link_name);
+    }
 
     switch (technology) {
     case Device::kEthernet: