rt
 - eth0 connected and UP, eth1 connected but DOWN
 - without this patch, following sequence would brick NIC:
      ifconfig eth0 down
      ifconfig eth1 up
      ifconfig eth1 down
      ethtool -A eth1 autoneg off rx on tx off
      ifconfig eth1 up
      ifconfig eth1 down
      ethtool -A eth1 autoneg on rx on tx on
      ifconfig eth1 up
      ifconfig eth1 down
      ifup eth0
      sleep 120  # or longer
      ethtool eth1
   Just in case, sequence to un-brick:
      ifconfig eth0 down
      ethtool -A eth1 autoneg off rx on tx off
      ifconfig eth1 up
      ifconfig eth1 down
      ifup eth0
 - with this patch: no TX timeout after "bricking" sequence above

Details:
 - The following register accesses have been identified as the ones
   causing the NIC to freeze in "bricking" sequence above:
    - write NVREG_TX_PAUSEFRAME_ENABLE_V1 to eth1's register NvRegTxPauseFrame
    - write NVREG_MISC1_PAUSE_TX | NVREG_MISC1_FORCE to eth1's register NvRegMisc1
    - write 0 to eth1's register NvRegTransmitterControl
   This is what this patch avoids.

Signed-off-by: David Decotigny <decot@googlers.com>
Signed-off-by: David S. Miller <davem@davemloft.net>