netfilter: replace old NF_ARP calls with NFPROTO_ARP

(Supplements: ee999d8b9573df1b547aacdc6d79f86eb79c25cd)

NFPROTO_ARP actually has a different value from NF_ARP, so ensure all
callers use the new value so that packets _do_ get delivered to the
registered hooks.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>