net/virtio: introduce helper for clearing net header
net/virtio: introduce helper for clearing net header

This patch introduces a helper for clearing the virtio net header
to avoid the code duplication. Macro is used as it shows slightly
better performance.

Signed-off-by: Tiwei Bie <f338cf29d7d69ff1bc99f755ebfb0eb0accd409e@intel.com>
Reviewed-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk