bpf: Fix memlock accounting for sock_hash

Add missed bpf_map_charge_init() in sock_hash_alloc() and
correspondingly bpf_map_charge_finish() on ENOMEM.

It was found accidentally while working on unrelated selftest that
checks "map->memory.pages > 0" is true for all map types.

Before:
	# bpftool m l
	...
	3692: sockhash  name m_sockhash  flags 0x0
		key 4B  value 4B  max_entries 8  memlock 0B

After:
	# bpftool m l
	...
	84: sockmap  name m_sockmap  flags 0x0
		key 4B  value 4B  max_entries 8  memlock 4096B

Fixes: 604326b ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200612000857.2881453-1-rdna@fb.com

net/core/sock_map.c

@@ -991,11 +991,15 @@ static struct bpf_map *sock_hash_alloc(union bpf_attr *attr)
 		err = -EINVAL;
 		goto free_htab;
 	}
+	err = bpf_map_charge_init(&htab->map.memory, cost);
+	if (err)
+		goto free_htab;
 
 	htab->buckets = bpf_map_area_alloc(htab->buckets_num *
 					   sizeof(struct bpf_htab_bucket),
 					   htab->map.numa_node);
 	if (!htab->buckets) {
+		bpf_map_charge_finish(&htab->map.memory);
 		err = -ENOMEM;
 		goto free_htab;
 	}