nexthop: Fix data-races around nexthop_compat_mode.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2149949


Upstream Status: linux.git

commit bdf00bf2
Author: Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Mon Jul 11 17:15:33 2022 -0700

    nexthop: Fix data-races around nexthop_compat_mode.

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

    Fixes: 4f80116d ("net: ipv4: add sysctl for nexthop api compatibility mode")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Guillaume Nault <gnault@redhat.com>