bonding: commit link status change after propose

Commit de77ecd4 ("bonding: improve link-status update in mii-monitoring")
moves link status commitment into bond_mii_monitor(), but it still relies
on the return value of bond_miimon_inspect() as the hint. We need to return
non-zero as long as we propose a link status change.

Fixes: de77ecd4 ("bonding: improve link-status update in mii-monitoring")
Reported-by: Benjamin Gilbert <benjamin.gilbert@coreos.com>
Tested-by: Benjamin Gilbert <benjamin.gilbert@coreos.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>