ARM: imx: configs: enable netfilter support

The Netfilter packet filtering framework is useful for so many
use cases that most people will build kernels with it enabled.

So, it would probably make sense to have it enabled by default.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>