xfrm: do not call rcu_read_unlock when afinfo is NULL in xfrm_get_tos

When xfrm_policy_get_afinfo returns NULL, it will not hold rcu
read lock. In this case, rcu_read_unlock should not be called
in xfrm_get_tos, just like other places where it's calling
xfrm_policy_get_afinfo.

Fixes: f5e2bb4f ("xfrm: policy: xfrm_get_tos cannot fail")
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_policy.c

@@ -1458,10 +1458,13 @@ xfrm_tmpl_resolve(struct xfrm_policy **pols, int npols, const struct flowi *fl,
 static int xfrm_get_tos(const struct flowi *fl, int family)
 {
 	const struct xfrm_policy_afinfo *afinfo;
-	int tos = 0;
+	int tos;
 
 	afinfo = xfrm_policy_get_afinfo(family);
-	tos = afinfo ? afinfo->get_tos(fl) : 0;
+	if (!afinfo)
+		return 0;
+
+	tos = afinfo->get_tos(fl);
 
 	rcu_read_unlock();