rtsold: Log messages about unexpected RAs at LOG_DEBUG.

Because rtsold listens for RAs on a raw socket, it may receive RAs from
interfaces that it does not manage. Such events can result in excessive
logging.

Submitted by:	Franco Fichtner <franco@opnsense.org>
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D8108

usr.sbin/rtsold/rtsol.c

@@ -347,7 +347,7 @@ rtsol_input(int s)
 	/* xxx: more validation? */
 
 	if ((ifi = find_ifinfo(pi->ipi6_ifindex)) == NULL) {
-		warnmsg(LOG_INFO, __func__,
+		warnmsg(LOG_DEBUG, __func__,
 		    "received RA from %s on an unexpected IF(%s)",
 		    inet_ntop(AF_INET6, &from.sin6_addr, ntopbuf,
 			sizeof(ntopbuf)),