kni: fix build with vhost header enabled

kni: fix build with vhost header enabled

A missing port from memcpy_toiovecend to copy_to_iter
is showed when vHost HDR is enabled. DPDK would not build.

This patch add this validation to build with kernel > 3.19.

Fixes: 45e63ba8db31 ("kni: fix vhost build with kernels 3.19 and 4.0")
Linux: ba7438aed924 ("vhost: don't bother copying iovecs in handle_rx(), kill memcpy_toiovecend()")

Signed-off-by: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>