bonding: convert arp_ip_target to use the new option API

This patch adds the necessary changes so arp_ip_target would use
the new bonding option API. This option is an exception because of
the way it's currently implemented that's why its netlink code is
a bit different from the other options to keep the functionality as
before and at the same time to have a single set function.

This patch also fixes a few stylistic errors.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>