network/ifup.sh: arping for static IPv4 addresses

modules.d/40network/ifup.sh

@@ -163,6 +163,10 @@ do_static() {
         ip addr add $ip/$mask ${srv:+peer $srv} dev $netif
         wait_for_ipv6_dad $netif
     else
+        if ! arping -f -q -D -c 2 -I $netif $ip; then
+            warn "Duplicate address detected for $ip for interface $netif."
+            return 1
+        fi
         ip addr flush dev $netif
         ip addr add $ip/$mask ${srv:+peer $srv} brd + dev $netif
     fi