bonding: convert num_peer_notif to use the new option API

This patch adds the necessary changes so num_peer_notif would use
the new bonding option API.
When the auto-sysfs generation is done an alias should be added for
this option as there're currently 2 entries in sysfs for it.

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