ieee802154: 6lowpan: set IFF_NO_QUEUE

This patch sets the IFF_NO_QUEUE for IEEE 802.15.4 6lowpan interfaces. As
commit 24dcbf66

 ("6lowpan: Don't set IFF_NO_QUEUE") removes it for
"reasons" from the bluetooth 6lowpan subsystem. In IEEE 802.15.4 the lower
interface deals with one qdisc for the real hardware, 6LoWPAN does the
protocol adaption only and no second queuing on top.

Signed-off-by: Alexander Aring <aring@mojatatu.com>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>