Documentation: bareudp: update iproute2 sample commands

bareudp.rst was written before iproute2 gained support for this new
type of tunnel. Therefore, the sample command lines didn't match the
final iproute2 implementation.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>