xfrm: don't call xfrm_policy_cache_flush under xfrm_state_lock

I might be wrong but it doesn't look like xfrm_state_lock is required
for xfrm_policy_cache_flush and calling it under this lock triggers both
"sleeping function called from invalid context" and "possible circular
locking dependency detected" warnings on flush.

Fixes: ec30d78c xfrm: add xdst pcpu cache
Signed-off-by: Artem Savkov <asavkov@redhat.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_state.c

@@ -732,12 +732,12 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
 			}
 		}
 	}
+out:
+	spin_unlock_bh(&net->xfrm.xfrm_state_lock);
 	if (cnt) {
 		err = 0;
 		xfrm_policy_cache_flush();
 	}
-out:
-	spin_unlock_bh(&net->xfrm.xfrm_state_lock);
 	return err;
 }
 EXPORT_SYMBOL(xfrm_state_flush);