ipv6: fix the use of pcpu_tstats in sit

when read/write the 64bit data, the correct lock should be hold.

Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Keith <javelinanddart@gmail.com>
Change-Id: Ie9c73149b86eb028e1646d1001bdb4310a72fe14
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>