net/ip6_tunnel: fix dst leak

the commit cdf3464e6c6b ("ipv6: Fix dst_entry refcnt bugs in ip6_tunnel")
introduced percpu storage for ip6_tunnel dst cache, but while clearing
such cache it used raw_cpu_ptr to walk the per cpu entries, so cached
dst on non current cpu are not actually reset.

This patch replaces raw_cpu_ptr with per_cpu_ptr, properly cleaning
such storage.

Fixes: cdf3464e6c6b ("ipv6: Fix dst_entry refcnt bugs in ip6_tunnel")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_tunnel.c

@@ -177,7 +177,7 @@ void ip6_tnl_dst_reset(struct ip6_tnl *t)
 	int i;
 
 	for_each_possible_cpu(i)
-		ip6_tnl_per_cpu_dst_set(raw_cpu_ptr(t->dst_cache), NULL);
+		ip6_tnl_per_cpu_dst_set(per_cpu_ptr(t->dst_cache, i), NULL);
 }
 EXPORT_SYMBOL_GPL(ip6_tnl_dst_reset);