staging: gdm724x: check for overflow in gdm_lte_netif_rx()

This code assumes that "len" is at least 62 bytes, but we need a check
to prevent a read overflow.

Fixes: 61e12104 ("staging: gdm7240: adding LTE USB driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YMcoTPsCYlhh2TQo@mwanda


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>