net: Fix a data-race around netdev_budget_usecs.

stable inclusion
from stable-v4.19.257
commit 2a341830849e1ced57e40455bcaa6fc9b79662d5
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5UQH4


CVE: NA

--------------------------------

[ Upstream commit fa45d484 ]

While reading netdev_budget_usecs, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its reader.

Fixes: 7acf8a1e ("Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>