cnic: Prevent "scheduling while atomic" when calling ->cnic_init()

cnic_dev_list is protected by rtnl_lock and cnic_dev_lock spin_lock during
modifications.  When looping on cnic_dev_list and calling ->cnic_init(),
we should just hold rtnl_lock since ->cnic_init() may sleep.

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