wilc1000: Rename tx task from "K_TXQ_TASK" to NETDEV-tx

This follows normal Linux conventions and is also more useful because
the netdevice name is part of the task name (e.g., "wlan0-tx" for
network device "wlan0").

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211209044411.3482259-4-davidm@egauge.net