drivers/net/wan/x25_asy: Correct the ndo_open and ndo_stop functions

drivers/net/wan/x25_asy: Correct the ndo_open and ndo_stop functions

1.
Move the lapb_register/lapb_unregister calls into the ndo_open/ndo_stop
functions.
This makes the LAPB protocol start/stop when the network interface
starts/stops. When the network interface is down, the LAPB protocol
shouldn't be running and the LAPB module shoudn't be generating control
frames.

2.
Move netif_start_queue/netif_stop_queue into the ndo_open/ndo_stop
functions.
This makes the TX queue start/stop when the network interface
starts/stops.
(netif_stop_queue was originally in the ndo_stop function. But to make
the code look better, I created a new function to use as ndo_stop, and
made it call the original ndo_stop function. I moved netif_stop_queue
from the original ndo_stop function to the new ndo_stop function.)

Cc: Martin Schiller <ms@dev.tdt.de>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>