if_media.c: use __FBSDID().

Reviewed by:	hselasky
Sponsored by:	Mellanox Technologies
Differential revision:	https://reviews.freebsd.org/D23620

sys/net/if_media.c

@@ -1,5 +1,4 @@
 /*	$NetBSD: if_media.c,v 1.1 1997/03/17 02:55:15 thorpej Exp $	*/
-/* $FreeBSD$ */
 
 /*-
  * SPDX-License-Identifier: BSD-4-Clause
@@ -48,6 +47,9 @@
  * to implement this interface.
  */
 
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
 #include "opt_ifmedia.h"
 
 #include <sys/param.h>