qtnfmac: support 64-bit network interface stats

On 32-bit platforms packet counters are stored in a net_device_stats struct
as unsigned long integers. As a result, after some time of network activity
an overflow takes place in network packet counters. This patch makes use of
new structs for holding interface statistics.

Signed-off-by: Vasily Ulyanov <vulyanov@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>