[XFRM] Statistics: Add outbound-dropping error.

o Increment PolError counter when flow_cache_lookup() returns
  errored pointer.

o Increment NoStates counter at larval-drop.
Signed-off-by: NMasahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/xfrm/xfrm_policy.c

@@ -1510,8 +1510,10 @@ int __xfrm_lookup(struct dst_entry **dst_p, struct flowi *fl,
 		policy = flow_cache_lookup(fl, dst_orig->ops->family,
 					   dir, xfrm_policy_lookup);
 		err = PTR_ERR(policy);
-		if (IS_ERR(policy))
+		if (IS_ERR(policy)) {
+			XFRM_INC_STATS(LINUX_MIB_XFRMOUTPOLERROR);
 			goto dropdst;
+		}
 	}
 
 	if (!policy)
@@ -1603,6 +1605,7 @@ int __xfrm_lookup(struct dst_entry **dst_p, struct flowi *fl,
 				/* EREMOTE tells the caller to generate
 				 * a one-shot blackhole route.
 				 */
+				XFRM_INC_STATS(LINUX_MIB_XFRMOUTNOSTATES);
 				xfrm_pol_put(policy);
 				return -EREMOTE;
 			}