eth: alx: take rtnl_lock on resume

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

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:

__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.