usb/net: rndis: fixup a few name prefixes

This switches a horde of NDIS_*-prefixed variables to the RNDIS_*
prefix. Most of them aren't used much and causes no changes.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>