vlan: 64 bit rx counters

Use u64_stats_sync infrastructure to implement 64bit rx stats.

(tx stats are addressed later)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>