Linux network drivers normally disallow changing the MAC address when
the interface is up.  This driver has been different in that it allows
to change the MAC address *only* when it's up.  This patch brings
wilc1000 behavior more in line with other network drivers.  We could
have replaced wilc_set_mac_addr() with eth_mac_addr() but that would
break existing documentation on how to change the MAC address.
Likewise, return -EADDRNOTAVAIL (not -EINVAL) when the specified MAC
address is invalid or unavailable.

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210303194846.1823596-1-davidm@egauge.net