use bridge interface for arping if interface is in the bridge

In case of bridge kernel uses bridge MAC for regular packets.
arping doesn't check routing decision and in case of passing
interface from the bridge it will use interface MAC as source.
This might produce conflicting ARP entry on other side, because
same IP has bridge MAC and at the same time interface MAC which
might differ.

src/neigh.c

@@ -493,14 +493,20 @@ static void neigh_probing_timer_run(atimer_t *t)
 	getcurrtime(&now);
 
 	list_for_each_entry(x, &e->iplist, list) {
+		char mifname[16] = {0};
 		char cmd[256] = {0};
 		char ipbuf[46] = {0};
+		int mifindex = 0;
 
 		if (x->ip.family != AF_INET)
 			continue;
 
 		inet_ntop(x->ip.family, &x->ip.addr, ipbuf, sizeof(ipbuf));
-		snprintf(cmd, 255, "arping -q -I %s -c 1 -w 1 -f %s &", e->ifname, ipbuf);
+		mifindex = if_isbridge_interface(e->ifname);
+		if (mifindex > 0 && if_indextoname(mifindex, mifname))
+			snprintf(cmd, 255, "arping -q -I %s -c 1 -w 1 -f %s &", mifname, ipbuf);
+		else
+			snprintf(cmd, 255, "arping -q -I %s -c 1 -w 1 -f %s &", e->ifname, ipbuf);
 		dbg("[%jd.%jd]  %s\n", (uintmax_t)now.tv_sec, (uintmax_t)now.tv_usec, cmd);
 		runCmd(cmd); /* Flawfinder: ignore */
 	}