bonding: ratelimit failed speed/duplex update warning

bond_miimon_commit() handles the UP transition for each slave of a bond
in the case of MII. It is triggered 10 times per second for the default
MII Polling interval of 100ms. For device drivers that do not implement
__ethtool_get_link_ksettings() the call to bond_update_speed_duplex()
fails persistently while the MII status could remain UP. That is, in
this and other cases where the speed/duplex update keeps failing over a
longer period of time while the MII state is UP, a warning is printed
every MII polling interval.

To address these excessive warnings net_ratelimit() should be used.
Printing a warning once would not be sufficient since the call to
bond_update_speed_duplex() could recover to succeed and fail again
later. In that case there would be no new indication what went wrong.

Fixes: b5bf0f5b

 (bonding: correctly update link status during mii-commit phase)
Signed-off-by: Andreas Born <futur.andy@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>