macvlan: play well with ipvlan device

If device is already used as an ipvlan port then refuse to
use it as a macvlan port at early stage of port creation.

	thost1:~# ip link add link eth0 ipvl0 type ipvlan
	thost1:~# echo $?
	0
	thost1:~# ip link add link eth0 mvl0 type macvlan
	RTNETLINK answers: Device or resource busy
	thost1:~# echo $?
	2
	thost1:~#

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>