include interface name in rad error message

[Claudio Jeker]

In my syslog I have this:
    rad[83563]: RA from non link local address ::
now it would be splendid to know on which of the 4 interfaces rad is
operating on this happened. So here is a diff doing that.

-- 
:wq Claudio

Index: engine.c
===================================================================
RCS file: /cvs/src/usr.sbin/rad/engine.c,v
retrieving revision 1.15
diff -u -p -r1.15 engine.c
--- engine.c    15 Mar 2019 16:47:19 -0000      1.15
+++ engine.c    20 May 2020 07:09:32 -0000
@@ -482,7 +482,8 @@ parse_rs(struct imsg_ra_rs *rs)
        len = rs->len;
 
        if (!IN6_IS_ADDR_LINKLOCAL(&rs->from.sin6_addr)) {
-               log_warnx("RA from non link local address %s", hbuf);
+               log_warnx("RA from non link local address %s on %s", hbuf,
+                   if_indextoname(rs->if_index, ifnamebuf));
                return;
        }