mac-telnet: mark uci as conffile

Fixes: 8399121e6 ("mac-telnet: install uci as config file")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

net/mac-telnet/Makefile

@@ -63,6 +63,10 @@ define Package/mac-telnet-server/install-extra
 	$(INSTALL_CONF) ./files/mactelnet.config $$(1)/etc/config/mactelnet
 endef
 
+define Package/mac-telnet-server/conffiles
+/etc/config/mactelnet
+endef
+
 
 $(eval $(call BuildPlugin,server,mactelnetd))
 $(eval $(call BuildPlugin,client,mactelnet))