ethernet_interface: Add INFO message for config writes

Change-Id: Id65a8797e15af13d1efc9208429134192989669c
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/ethernet_interface.cpp b/src/ethernet_interface.cpp
index 77e5df1..8700d05 100644
--- a/src/ethernet_interface.cpp
+++ b/src/ethernet_interface.cpp
@@ -1141,6 +1141,8 @@
     writeDHCPSection(stream);
 
     stream.close();
+    auto msg = fmt::format("Wrote networkd file: {}", confPath.native());
+    log<level::INFO>(msg.c_str(), entry("FILE=%s", confPath.c_str()));
 }
 
 void EthernetInterface::writeDHCPSection(std::fstream& stream)