drivers: ethernet: stm32, sam, mcux: correctly set LAA bit

When randomly generating MAC addresses they will always be
locally administrated addresses, so the LAA bit should be set.
The LAA bit is the 2nd bit of the 1st byte of the MAC address
not the 2nd bit of the 4th byte.

Fixes: #16452

Signed-off-by: Erwin Rol <erwin@erwinrol.com>