8021q: update description

Replace deprecated 'vconfig' tool with 'ip' from 'iproute2'. Add
some beautifications like replacing 'ethernet' with 'Ethernet' and
removing unneeded spaces.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>