netfilter: arp_tables: fix IEEE1394 ARP payload mangling

sashiko.dev noticed that similar bug pattern exists in arpt_mangle:
  "IEEE1394 ARP payloads omit the target hardware address, advancing
  arpptr by hln after the source IP address skips over the actual target
  IP address."

Apply similar fix: check dev->type.  If we're asked to mangle what
doesn't exist, drop the packet.

Fixes: 6752c8db8e0c ("firewire net, ipv4 arp: Extend hardware address and remove driver-level packet inspection.")
Signed-off-by: Florian Westphal <fw@strlen.de>