netlink: Add common function for extracting payload

Change-Id: I809bd17d50ccb8a8f624b6117c088193f55e79de
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/neighbor.cpp b/src/neighbor.cpp
index cfa8e60..58e1a47 100644
--- a/src/neighbor.cpp
+++ b/src/neighbor.cpp
@@ -35,7 +35,7 @@
     {
         throw std::runtime_error("Not a neighbor msg");
     }
-    auto ndm = stdplus::raw::extract<ndmsg>(msg);
+    const auto& ndm = netlink::extractRtData<ndmsg>(msg);
 
     // Filter out neighbors we don't care about
     unsigned ifindex = ndm.ndm_ifindex;