This contains a more advanced version of parse_ethhdr() named
__parse_ethhdr_vlan(), that will populate an array of VLAN ids
while walking the VLAN headers.

Again it turns out, that the compile can figure out if this
expansion of code is actually needed or not.  This this example
is mostly to point out the experiences with the LLVM optimizer.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>