net: hns3: fix deadlock issue when externel_lb and reset are executed together

In the Linux kernel, the following vulnerability has been resolved:

net: hns3: fix deadlock issue when externel_lb and reset are executed together

When externel_lb and reset are executed together, a deadlock may
occur:
[ 3147.217009] INFO: task kworker/u321:0:7 blocked for more than 120 seconds.
[ 3147.230483] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 3147.238999] task:kworker/u321:0 state:D stack: 0 pid: 7 ppid: 2 flags:0x00000008
[ 3147.248045] Workqueue: hclge hclge_service_task [hclge]
[ 3147.253957] Call trace:
[ 3147.257093] __switch_to+0x7c/0xbc
[ 3147.261183] __schedule+0x338/0x6f0
[ 3147.265357] schedule+0x50/0xe0
[ 3147.269185] schedule_preempt_disabled+0x18/0x24
[ 3147.274488] __mutex_lock.constprop.0+0x1d4/0x5dc
[ 3147.279880] __mutex_lock_slowpath+0x1c/0x30
[ 3147.284839] mutex_lock+0x50/0x60
[ 3147.288841] rtnl_lock+0x20/0x2c
[ 3147.292759] hclge_reset_prepare+0x68/0x90 [hclge]
[ 3147.298239] hclge_reset_subtask+0x88/0xe0 [hclge]
[ 3147.303718] hclge_reset_service_task+0x84/0x120 [hclge]
[ 3147.309718] hclge_service_task+0x2c/0x70 [hclge]
[ 3147.315109] process_one_work+0x1d0/0x490
[ 3147.319805] worker_thread+0x158/0x3d0
[ 3147.324240] kthread+0x108/0x13c
[ 3147.328154] ret_from_fork+0x10/0x18

In externel_lb process, the hns3 driver call napi_disable()
first, then the reset happen, then the restore process of the
externel_lb will fail, and will not call napi_enable(). When
doing externel_lb again, napi_disable() will be double call,
cause a deadlock of rtnl_lock().

This patch use the HNS3_NIC_STATE_DOWN state to protect the
calling of napi_disable() and napi_enable() in externel_lb
process, just as the usage in ndo_stop() and ndo_start().