rtnetlink: Migrate IP functions

Change-Id: I4c87b59306911df4c5a73e441b2b962fbaab072c
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/rtnetlink.hpp b/src/rtnetlink.hpp
index 41df902..48f3820 100644
--- a/src/rtnetlink.hpp
+++ b/src/rtnetlink.hpp
@@ -7,6 +7,10 @@
 
 namespace phosphor::network::netlink
 {
+
 std::optional<std::tuple<unsigned, InAddrAny>>
     gatewayFromRtm(std::string_view msg);
-}
+
+AddressInfo addrFromRtm(std::string_view msg);
+
+} // namespace phosphor::network::netlink