net/mlx5e: Prevent deadlock while disabling aRFS

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

net/mlx5e: Prevent deadlock while disabling aRFS

When disabling aRFS under the `priv->state_lock`, any scheduled
aRFS works are canceled using the `cancel_work_sync` function,
which waits for the work to end if it has already started.
However, while waiting for the work handler, the handler will
try to acquire the `state_lock` which is already acquired.

The worker acquires the lock to delete the rules if the state
is down, which is not the worker's responsibility since
disabling aRFS deletes the rules.

Add an aRFS state variable, which indicates whether the aRFS is
enabled and prevent adding rules when the aRFS is disabled.

Kernel log:

======================================================
WARNING: possible circular locking dependency detected
6.7.0-rc4_net_next_mlx5_5483eb2 #1 Tainted: G I
------------------------------------------------------
ethtool/386089 is trying to acquire lock:
ffff88810f21ce68 ((work_completion)(&rule->arfs_work)){+.+.}-{0:0}, at: __flush_work+0x74/0x4e0

but task is already holding lock:
ffff8884a1808cc0 (&priv->state_lock){+.+.}-{3:3}, at: mlx5e_ethtool_set_channels+0x53/0x200 [mlx5_core]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&priv->state_lock){+.+.}-{3:3}:
__mutex_lock+0x80/0xc90
arfs_handle_work+0x4b/0x3b0 [mlx5_core]
process_one_work+0x1dc/0x4a0
worker_thread+0x1bf/0x3c0
kthread+0xd7/0x100
ret_from_fork+0x2d/0x50
ret_from_fork_asm+0x11/0x20

-> #0 ((work_completion)(&rule->arfs_work)){+.+.}-{0:0}:
__lock_acquire+0x17b4/0x2c80
lock_acquire+0xd0/0x2b0
__flush_work+0x7a/0x4e0
__cancel_work_timer+0x131/0x1c0
arfs_del_rules+0x143/0x1e0 [mlx5_core]
mlx5e_arfs_disable+0x1b/0x30 [mlx5_core]
mlx5e_ethtool_set_channels+0xcb/0x200 [mlx5_core]
ethnl_set_channels+0x28f/0x3b0
ethnl_default_set_doit+0xec/0x240
genl_family_rcv_msg_doit+0xd0/0x120
genl_rcv_msg+0x188/0x2c0
netlink_rcv_skb+0x54/0x100
genl_rcv+0x24/0x40
netlink_unicast+0x1a1/0x270
netlink_sendmsg+0x214/0x460
__sock_sendmsg+0x38/0x60
__sys_sendto+0x113/0x170
__x64_sys_sendto+0x20/0x30
do_syscall_64+0x40/0xe0
entry_SYSCALL_64_after_hwframe+0x46/0x4e

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&priv->state_lock);
lock((work_completion)(&rule->arfs_work));
lock(&priv->state_lock);
lock((work_completion)(&rule->arfs_work));

*** DEADLOCK ***

3 locks held by ethtool/386089:
#0: ffffffff82ea7210 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40
#1: ffffffff82e94c88 (rtnl_mutex){+.+.}-{3:3}, at: ethnl_default_set_doit+0xd3/0x240
#2: ffff8884a1808cc0 (&priv->state_lock){+.+.}-{3:3}, at: mlx5e_ethtool_set_channels+0x53/0x200 [mlx5_core]

stack backtrace:
CPU: 15 PID: 386089 Comm: ethtool Tainted: G I 6.7.0-rc4_net_next_mlx5_5483eb2 #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x60/0xa0
check_noncircular+0x144/0x160
__lock_acquire+0x17b4/0x2c80
lock_acquire+0xd0/0x2b0
? __flush_work+0x74/0x4e0
? save_trace+0x3e/0x360
? __flush_work+0x74/0x4e0
__flush_work+0x7a/0x4e0
? __flush_work+0x74/0x4e0
? __lock_acquire+0xa78/0x2c80
? lock_acquire+0xd0/0x2b0
? mark_held_locks+0x49/0x70
__cancel_work_timer+0x131/0x1c0
? mark_held_locks+0x49/0x70
arfs_del_rules+0x143/0x1e0 [mlx5_core]
mlx5e_arfs_disable+0x1b/0x30 [mlx5_core]
mlx5e_ethtool_set_channels+0xcb/0x200 [mlx5_core]
ethnl_set_channels+0x28f/0x3b0
ethnl_default_set_doit+0xec/0x240
genl_family_rcv_msg_doit+0xd0/0x120
genl_rcv_msg+0x188/0x2c0
? ethn
---truncated---