drivers/usbdev: Fix buffer overrun check in rndis.c
The rndis driver has been working since 13 Nov 2017.
However, I finally found that it depends on network and buffer
configurations. If a receiving TCP packet is devided into smaller
ones based on USB max packet size, this condition check works
correctly.
Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>
Approved-by: GregoryN <gnutt@nuttx.org>