nft: arp: add parse_target to nft_family_ops_arp

This patch adds parse_target for arp family, fixing segfaults
for xtables-arp -L after rules like:

	xtables-arp -A OUTPUT -o eth0 -j CLASSIFY --set-class 0:7
	xtables-arp -A OUTPUT -o eth1 --h-length 6 \
		-j mangle --mangle-mac-s 01:00:5e:00:01:01

Signed-off-by: Giuseppe Longo <giuseppelng@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/iptables/nft-arp.c b/iptables/nft-arp.c
index 570962d..08f8814 100644
--- a/iptables/nft-arp.c
+++ b/iptables/nft-arp.c
@@ -643,4 +643,5 @@
 	.print_firewall		= nft_arp_print_firewall,
 	.post_parse		= NULL,
 	.rule_find		= nft_arp_rule_find,
+	.parse_target		= nft_arp_parse_target,
 };