Fix nftables / device rename race on boot

On some boots nftables would start before udev had renamed the wan0
device, causing the service to fail to start.

Using 'oifname' instead of 'oif' allows the creation of nftables rules
for device that don't exist.

etc/nftables.conf

@@ -5,7 +5,7 @@ table ip filter {
 	chain forward {
 		type filter hook forward priority 0; policy drop;
 		ct state established,related counter accept
-		iifname "br0" oif "wan0" counter accept
+		iifname "br0" oifname "wan0" counter accept
 	}
 
 	chain output {
@@ -40,6 +40,6 @@ table ip nat {
 
 	chain postrouting {
 		type nat hook postrouting priority 100; policy accept;
-		oif "wan0" counter masquerade
+		oifname "wan0" counter masquerade
 	}
 }