myri10ge: ensure tx queues remain stopped

Ensure that our tx queues remain stopped when we stop them in
myri10ge_close().  Not doing so can potentially lead to traffic being
transmitted when the interface is removed, which can lead to NULL
pointer dereferences.

Signed-off-by: Jon Mason <mason@myri.com>
Signed-off-by: David S. Miller <davem@davemloft.net>