transport/usb: Fix potential buffer overrun
transport/usb: Fix potential buffer overrun

When HCI command was received from USB transport cmd_len was not checked
and was used for memcpy.
It could lead to memory corruption if USB stack called this function with
size exceeding maximum command size. This is currently possible scenario
with TinyUSB stack (it will be fixed there as well).

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble