rsyslog-config: fix compile warnings under -Werror

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I13081a2f5e98a76cbc708ad1c987ee76e311c6ae
diff --git a/phosphor-rsyslog-config/server-conf.hpp b/phosphor-rsyslog-config/server-conf.hpp
index 8e1b2cb..979f845 100644
--- a/phosphor-rsyslog-config/server-conf.hpp
+++ b/phosphor-rsyslog-config/server-conf.hpp
@@ -106,7 +106,7 @@
     /** @brief React to hostname change
      *  @param[in] msg - sdbusplus message
      */
-    void hostnameChanged(sdbusplus::message::message& msg)
+    void hostnameChanged(sdbusplus::message::message& /*msg*/)
     {
         restart();
     }