ipv4: convert fib_num_tclassid_users to atomic_t

stable inclusion
from stable-v5.10.84
commit 9a40a1e0eb50c49bee7286126341937c136c78f3
bugzilla: 186030 https://gitee.com/openeuler/kernel/issues/I4QV2F

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a40a1e0eb50c49bee7286126341937c136c78f3



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

commit 213f5f8f upstream.

Before commit faa041a4 ("ipv4: Create cleanup helper for fib_nh")
changes to net->ipv4.fib_num_tclassid_users were protected by RTNL.

After the change, this is no longer the case, as free_fib_info_rcu()
runs after rcu grace period, without rtnl being held.

Fixes: faa041a4 ("ipv4: Create cleanup helper for fib_nh")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: David Ahern <dsahern@kernel.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>