linux-boundary: freescale 4.0.0 BSP release

Boundary Devices kernel release to follow up the Freescale v4.0.0
Use nitrogen6x_defconfig and enable CONFIG_NETFILTER.

Change-Id: Id7abac7267680690364769bb8b3d5c48947abab5
Signed-off-by: Jeremy Stashluk <jstashluk@dekaresearch.com>
Acked-by: Eric Nelson <eric.nelson@boundarydevices.com>