rtsold: lower log level of spurious message

When rtsold with `-d' it is supposed to show informal messages,
though it actually picks up prefix delegation RAs on other non-
configured interfaces.  Since it's listening on a raw socket,
we get all those things, but there's no misconfiguration and
no interest in what happens with other interfaces per se and
the debug level shall be sufficient.

PR: https://forum.opnsense.org/index.php?topic=3392

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)),