bluetooth: driver API update

Convert to net_device_ops and use internal net_device_stats in bnep
device. 

Note: no need for bnep_net_ioctl since if ioctl is not set, then
dev_ifsioc handles it by returning -EOPNOTSUPP

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: David S. Miller <davem@davemloft.net>