[Intel-wired-lan] Documentation: networking: ixgb: Remove reference to IXGB_NAPI

[Brown, Aaron F]

> NAPI is enabled by default and IXGB_NAPI was removed since
> commit 6d37ab282e24 ("ixgb: make NAPI the only option and the default")
> Update the doc accordingly.

> Signed-off-by: Corentin Labbe <clabbe at baylibre.com>
> ---
>  Documentation/networking/ixgb.txt | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
I'm sure I applied a "Tested-by:" on this before, but it's not showing in patchwork so...

Tested-by: Aaron Brown <aaron.f.brown at intel.com>