bonding: convert fail_over_mac to use the new option API

This patch adds the necessary changes so fail_over_mac would use
the new bonding option API. Also fixes a trivial copy/paste error in
bond_check_params where the wrong variable was used for the error msg.

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