net: Fix data-races around sysctl_devconf_inherit_init_net.

[ Upstream commit a5612ca1 ]

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

Fixes: 856c395c

 ("net: introduce a knob to control whether to inherit devconf config")
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>