net: moxa: MAC address reading, generating, validity checking

net: moxa: MAC address reading, generating, validity checking

This device does not remember its MAC address, so add a possibility
to get it from the platform. If it fails, generate a random address.
This will provide a MAC address early during boot without user space
being involved.

Also remove extra calls to is_valid_ether_addr().

Made after suggestions by Andrew Lunn:
1) Use eth_hw_addr_random() to assign a random MAC address during probe.
2) Remove is_valid_ether_addr() from moxart_mac_open()
3) Add a call to platform_get_ethdev_address() during probe
4) Remove is_valid_ether_addr() from moxart_set_mac_address(). The core does this

v1 -> v2:
Handle EPROBE_DEFER returned from platform_get_ethdev_address().
Move MAC reading code to the beginning of the probe function.

Signed-off-by: Sergei Antonov <[email protected]>
Suggested-by: Andrew Lunn <[email protected]>
CC: Yang Yingliang <[email protected]>
CC: Pavel Skripkin <[email protected]>
CC: Guobin Huang <[email protected]>
CC: Yang Wei <[email protected]>
CC: Christophe JAILLET <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
Reviewed-by: Vladimir Oltean <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>