The simple transmission mode was treating the area immediately after the
transmit command block (TCB) as if it were a transmit buffer descriptor,
when in reality it is simply the packet data. This change simply copies
the data following the TCB into the packet buffer.

Signed-off-by: Mike Nawrocki <michael.nawrocki@gtri.gatech.edu>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>