Add back missing copyright and license statement. This is identical

to the statement in ip_mroute.h, as well as being the same as what
OpenBSD has done with this file.  It matches the copyright in NetBSD's
1.1 through 1.14 versions of the file as well, which they subsequently
added back.

It appears to have been lost in the 4.4-lite1 import for FreeBSD 2.0,
but where and why I've not investigated further.  OpenBSD had the same
problem.  NetBSD had a copyright notice until Multicast 3.5 was
integrated verbatim back in 1995.  This appears to be the version that
made it into 4.4-lite1.

Approved by: re (scottl)
MFC after: 3 days

sys/netinet/ip_mroute.c

@@ -1,3 +1,38 @@
+/*-
+ * Copyright (c) 1989 Stephen Deering
+ * Copyright (c) 1992, 1993
+ *      The Regents of the University of California.  All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * Stephen Deering of Stanford University.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *      @(#)ip_mroute.c 8.2 (Berkeley) 11/15/93
+ */
+
 /*
  * IP multicast forwarding procedures
  *