net: add net poll support for atl2 driver

Add netconsole support for Atheros L2 10/100 network device.

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Acked-by: Jay Cliburn <jacliburn@bellsouth.net>
Signed-off-by: David S. Miller <davem@davemloft.net>