nvme-tcp: use __dev_get_by_name instead dev_get_by_name for OPT_HOST_IFACE

dev_get_by_name() finds network device by name but it also increases the
reference count.

If a nvme-tcp queue is present and the network device driver is removed
before nvme_tcp, we will face the following continuous log:

  "kernel:unregister_netdevice: waiting for <eth> to become free. Usage count = 2"

And rmmod further halts. Similar case arises during reboot/shutdown
with nvme-tcp queue present and both never completes.

To fix this, use __dev_get_by_name() which finds network device by
name without increasing any reference counter.

Fixes: 3ede8f72 ("nvme-tcp: allow selecting the network interface for connections")
Signed-off-by: Omkar Kulkarni <okulkarni@marvell.com>
Signed-off-by: Shai Malin <smalin@marvell.com>
Signed-off-by: Prabhakar Kushwaha <pkushwaha@marvell.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
[hch: remove the ->ndev member entirely]
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/tcp.c

@@ -123,7 +123,6 @@ struct nvme_tcp_ctrl {
 	struct blk_mq_tag_set	admin_tag_set;
 	struct sockaddr_storage addr;
 	struct sockaddr_storage src_addr;
-	struct net_device	*ndev;
 	struct nvme_ctrl	ctrl;
 
 	struct work_struct	err_work;
@@ -2533,8 +2532,7 @@ static struct nvme_ctrl *nvme_tcp_create_ctrl(struct device *dev,
 	}
 
 	if (opts->mask & NVMF_OPT_HOST_IFACE) {
-		ctrl->ndev = dev_get_by_name(&init_net, opts->host_iface);
-		if (!ctrl->ndev) {
+		if (!__dev_get_by_name(&init_net, opts->host_iface)) {
 			pr_err("invalid interface passed: %s\n",
 			       opts->host_iface);
 			ret = -ENODEV;