6lowpan: fix lockdep splats

6lowpan: fix lockdep splats

[ Upstream commit 20e7c4e80dcd01dad5e6c8b32455228b8fe9c619 ]

When a device ndo_start_xmit() calls again dev_queue_xmit(),
lockdep can complain because dev_queue_xmit() is re-entered and the
spinlocks protecting tx queues share a common lockdep class.

Same issue was fixed for bonding/l2tp/ppp in commits

0daa2303028a6 ("[PATCH] bonding: lockdep annotation")
49ee49202b4ac ("bonding: set qdisc_tx_busylock to avoid LOCKDEP splat")
23d3b8bfb8eb2 ("net: qdisc busylock needs lockdep annotations ")
303c07db487be ("ppp: set qdisc_tx_busylock to avoid LOCKDEP splat ")

Reported-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>