USB: gadget: fix ethernet gadget crash in gether_setup

Crash is triggered by commit e6484930d7 ("net: allocate tx queues in
register_netdevice"), which moved tx netqueue creation into register_netdev.
So now calling netif_stop_queue() before register_netdev causes an oops.
Move netif_stop_queue() after net device registration to fix crash.

Signed-off-by: Dmitry Artamonow <mad_soft@inbox.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>