[legal] Add missing copyright header to net/ipv4.c

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/ipv4.c

+/*
+ * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
+ * Copyright (C) 2006 Nikhil Chandru Rao
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
 #include <string.h>
 #include <stdint.h>
 #include <stdlib.h>