bonding: fix out of range parameters for bond_intmax_tbl

I've missed to add a NULL entry to the bond_intmax_tbl when I introduced
it with the conversion of arp_interval so add it now.

CC: Jay Vosburgh <j.vosburgh@gmail.com>
CC: Veaceslav Falico <vfalico@gmail.com>
CC: Andy Gospodarek <andy@greyhouse.net>

Fixes: 7bdb04ed ("bonding: convert arp_interval to use the new option API")
Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Acked-by: Veaceslav Falico <vfalico@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>