usb: gadget: f_ncm: Fix MAC assignment NCM ethernet

usb: gadget: f_ncm: Fix MAC assignment NCM ethernet

This fix is already present in f_ecm.c and was never
propagated to f_ncm.c

When creating multiple NCM ethernet devices
on a composite usb gadget device
each MAC address on the HOST side will be identical.
Having the same MAC on different network interfaces is bad.

This fix updates the MAC address inside the
ncm_strings_defs global during the ncm_bind call.
This ensures each device has a unique MAC.
In f_ecm.c ecm_string_defs is updated in the same way.

The defunct MAC assignment in ncm_alloc has been removed.

Signed-off-by: raub camaioni <raubcameo@gmail.com>
Link: https://lore.kernel.org/r/20250815131358.1047525-1-raubcameo@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>