eth: alx: take rtnl_lock on resume

Zbynek reports that alx trips an rtnl assertion on resume:

 RTNL: assertion failed at net/core/dev.c (2891)
 RIP: 0010:netif_set_real_num_tx_queues+0x1ac/0x1c0
 Call Trace:
  <TASK>
  __alx_open+0x230/0x570 [alx]
  alx_resume+0x54/0x80 [alx]
  ? pci_legacy_resume+0x80/0x80
  dpm_run_callback+0x4a/0x150
  device_resume+0x8b/0x190
  async_resume+0x19/0x30
  async_run_entry_fn+0x30/0x130
  process_one_work+0x1e5/0x3b0

indeed the driver does not hold rtnl_lock during its internal close
and re-open functions during suspend/resume. Note that this is not
a huge bug as the driver implements its own locking, and does not
implement changing the number of queues, but we need to silence
the splat.

Fixes: 4a5fe57e ("alx: use fine-grained locking instead of RTNL")
Reported-and-tested-by: Zbynek Michl <zbynek.michl@gmail.com>
Reviewed-by: Niels Dossche <dossche.niels@gmail.com>
Link: https://lore.kernel.org/r/20220928181236.1053043-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/atheros/alx/main.c

@@ -1912,11 +1912,14 @@ static int alx_suspend(struct device *dev)
 
 	if (!netif_running(alx->dev))
 		return 0;
+
+	rtnl_lock();
 	netif_device_detach(alx->dev);
 
 	mutex_lock(&alx->mtx);
 	__alx_stop(alx);
 	mutex_unlock(&alx->mtx);
+	rtnl_unlock();
 
 	return 0;
 }
@@ -1927,6 +1930,7 @@ static int alx_resume(struct device *dev)
 	struct alx_hw *hw = &alx->hw;
 	int err;
 
+	rtnl_lock();
 	mutex_lock(&alx->mtx);
 	alx_reset_phy(hw);
 
@@ -1943,6 +1947,7 @@ static int alx_resume(struct device *dev)
 
 unlock:
 	mutex_unlock(&alx->mtx);
+	rtnl_unlock();
 	return err;
 }