cnic: Improve NETDEV_UP event handling

During NETDEV_UP, we use symbol_get() to get the net driver's cnic
probe function.  This sometimes doesn't work if NETDEV_UP happens
right after NETDEV_REGISTER and the net driver is still running module
init code.  As a result, the cnic device may not be discovered.  We
fix this by probing on all NETDEV events if the device's netif_running
state is up.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>