Use netdev_alloc_pcpu_stats to allocate percpu stats and initialize syncp.

Fixes: 22e0f8b9 "net: sched: make bstats per cpu and estimator RCU safe"
Signed-off-by: NSabrina Dubroca <sd@queasysnail.net>
Acked-by: NCong Wang <cwang@twopensource.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>