vxge: Implement 64bit stats

vxge_get_stats() is racy, since it clears a block of memory (net_stats)
possibly still used by other cpus.

We can update this driver to full 64bit stats, since ndo_get_stats64()
provides a private block to store results, and driver maintains 64bit
counters already.

We also remove net_stats field from struct vxge_sw_stats

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Jon Mason <jon.mason@exar.com>
Signed-off-by: David S. Miller <davem@davemloft.net>