Documentation: fix wrong example command

In the IPVLAN documentation there is an example command line where the
master and slave interface names are inverted.
Fix the command line and also add the optional `name' keyword to better
describe what the command is doing.

v2: added commit message

Signed-off-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>