l2tp: fix return value check

In case of error, the function genlmsg_put() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should
be replaced with NULL test.

dpatch engine is used to auto generate this patch.
(https://github.com/weiyj/dpatch)
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/l2tp/l2tp_netlink.c

@@ -80,8 +80,8 @@ static int l2tp_nl_cmd_noop(struct sk_buff *skb, struct genl_info *info)
 
 	hdr = genlmsg_put(msg, info->snd_pid, info->snd_seq,
 			  &l2tp_nl_family, 0, L2TP_CMD_NOOP);
-	if (IS_ERR(hdr)) {
-		ret = PTR_ERR(hdr);
+	if (!hdr) {
+		ret = -EMSGSIZE;
 		goto err_out;
 	}
 
@@ -250,8 +250,8 @@ static int l2tp_nl_tunnel_send(struct sk_buff *skb, u32 pid, u32 seq, int flags,
 
 	hdr = genlmsg_put(skb, pid, seq, &l2tp_nl_family, flags,
 			  L2TP_CMD_TUNNEL_GET);
-	if (IS_ERR(hdr))
-		return PTR_ERR(hdr);
+	if (!hdr)
+		return -EMSGSIZE;
 
 	if (nla_put_u8(skb, L2TP_ATTR_PROTO_VERSION, tunnel->version) ||
 	    nla_put_u32(skb, L2TP_ATTR_CONN_ID, tunnel->tunnel_id) ||
@@ -617,8 +617,8 @@ static int l2tp_nl_session_send(struct sk_buff *skb, u32 pid, u32 seq, int flags
 	sk = tunnel->sock;
 
 	hdr = genlmsg_put(skb, pid, seq, &l2tp_nl_family, flags, L2TP_CMD_SESSION_GET);
-	if (IS_ERR(hdr))
-		return PTR_ERR(hdr);
+	if (!hdr)
+		return -EMSGSIZE;
 
 	if (nla_put_u32(skb, L2TP_ATTR_CONN_ID, tunnel->tunnel_id) ||
 	    nla_put_u32(skb, L2TP_ATTR_SESSION_ID, session->session_id) ||