Qemu-dm dumps core with the pcnet device. This patches fixes it.

Qemu-dm dumps core with the pcnet device. This patches fixes it.

When pcnet_receive calls pcnet_poll, which polls the receive and the send
rings. Whenever there is an element in the send ring that is owned by
the Lance chip it will call pcnet_transmit and send it. When the element
is the endp(acket), pcnet_transmit will copy it out, send the packet
(qemu_send_packet) and then clear the owner bit. Somewherer along the
qemu_send_packet execution path, pcnet_recieve is called again, which
calls pcnet_poll and starts this whole process again. This very rapidly
leads to a stack overflow and crashes qemu.

The fix is simple, stop the recursion. Once the packet is copied into
qemu datatstructure (before qemu_send_packet is called!), the owner bit
on the ring element should be cleared.

Signed-Off-By: Leendert van Doorn <leendert@watson.ibm.com>