staging: vt6655: don't stop TX queue unless buffer full.

Presently the TX buffer stops while filling the buffer.

However, this does not make use of the available buffer
space, it also lags the speed of the TX troughtput.

Only stop the queue when the buffer becomes full. The
Interupt handler will start the queue again when a
buffer is available.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>