fib_trie: Use empty_children instead of counting empty nodes in stats collection

It doesn't make much sense to count the pointers ourselves when
empty_children already has a count for the number of NULL pointers stored
in the tnode.  As such save ourselves the cycles and just use
empty_children.
Signed-off-by: NAlexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -1954,16 +1954,10 @@ static void trie_collect_stats(struct trie *t, struct trie_stat *s)
 			hlist_for_each_entry_rcu(li, &n->list, hlist)
 				++s->prefixes;
 		} else {
-			unsigned long i;
-
 			s->tnodes++;
 			if (n->bits < MAX_STAT_DEPTH)
 				s->nodesizes[n->bits]++;
-
-			for (i = tnode_child_length(n); i--;) {
-				if (!rcu_access_pointer(n->child[i]))
-					s->nullpointers++;
-			}
+			s->nullpointers += n->empty_children;
 		}
 	}
 	rcu_read_unlock();