bonding: fix active-backup transition after link failure

After the recent fix in commit 1899bb32 ("bonding: fix state
transition issue in link monitoring"), the active-backup mode with
miimon initially come-up fine but after a link-failure, both members
transition into backup state.

Following steps to reproduce the scenario (eth1 and eth2 are the
slaves of the bond):

    ip link set eth1 up
    ip link set eth2 down
    sleep 1
    ip link set eth2 up
    ip link set eth1 down
    cat /sys/class/net/eth1/bonding_slave/state
    cat /sys/class/net/eth2/bonding_slave/state

Fixes: 1899bb32 ("bonding: fix state transition issue in link monitoring")
CC: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>