bonding: options: remove bond->lock usage

We're safe to remove the bond->lock use from the arp targets because
arp_rcv_probe no longer acquires bond->lock, only rcu_read_lock.
Also setting the primary slave is safe because noone uses the bond->lock
as a syncing mechanism for that anymore.

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