scripts: fix ABI validator for KNI module config

scripts: fix ABI validator for KNI module config

The validator attempts to disable all kernel modules but since
commit 36080ff96b0eb37a6da8c4fec1a2f8a57dfadf5b fails to do so
for KNI, causing the build stage to fail if kernel headers are missing.

With the introduction of CONFIG_RTE_KNI_KMOD, CONFIG_RTE_LIBRTE_KNI=n
can eventually be dropped but leaving it around for now as its
needed with pre-2.1 versions.

Fixes: 36080ff96b0e ("config: add KNI kmod option")

Signed-off-by: Panu Matilainen <pmatilai@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>