Zheng Liang(lzheng@redhat.com) found a bug that if we config bonding with
arp monitor, sometimes bonding driver cannot get the speed and duplex from
its slaves, it will assume them to be 100Mb/sec and Full, please see
/proc/net/bonding/bond0.
But there is no such problem when uses miimon.

(Take igb for example)
I find that the reason is that after dev_open() in bond_enslave(),
bond_update_speed_duplex() will call igb_get_settings()
, but in that function,
it runs ethtool_cmd_speed_set(ecmd, -1); ecmd->duplex = -1;
because igb get an error value of status.
So even dev_open() is called, but the device is not really ready to get its
settings.

Maybe it is safe for us to call igb_get_settings() only after
this message shows up, that is "igb: p4p1 NIC Link is Up 1000 Mbps Full Duplex,
Flow Control: RX".

So I prefer to update the speed and duplex for a slave when reseices
NETDEV_CHANGE/NETDEV_UP event.

Changelog
V2:
1 remove the "fake 100/Full" logic in bond_update_speed_duplex(),
  set speed and duplex to -1 when it gets error value of speed and duplex.
2 delete the warning in bond_enslave() if bond_update_speed_duplex() returns
  error.
3 make bond_info_show_slave() handle bad values of speed and duplex.

Signed-off-by: Weiping Pan <wpan@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>