for this and return -1 when the spin lock fails.
The locking there should also properly protect against
set_multicast_list
- Context: BHs disabled
+ Context: Process with BHs disabled or BH (timer).
Notes: netif_queue_stopped() is guaranteed false
Interrupts must be enabled when calling hard_start_xmit.
(Interrupts must also be enabled when enabling the BH handler.)