arptables-nft-save: Fix position of -j option

arptables-nft-save: Fix position of -j option

Legacy arptables-save (just like arptables itself) prints verdict as
first option, then matches and finally any target options.

To achieve this without introducing double/trailing spaces everywhere,
integrate target ('-j') option printing into
nft_arp_print_rule_details() and make it print separating whitespace
before each option.

In nft_arp_save_rule(), replace the call to save_matches_and_target() by
by a direct call to cs->target->save() since the former prints '-j'
option itself. Since there are no match extensions in arptables, any
other code from that function is not needed.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>