RTL8139 ethernet controller in C+ mode supports multiple
descriptor rings, each with maximum of 64 descriptors. While
processing transmit descriptor ring in 'rtl8139_cplus_transmit',
it does not limit the descriptor count and runs forever. Add
check to avoid it.
Reported-by: NAndrew Henderson <hendersa@icculus.org>
Signed-off-by: NPrasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: NJason Wang <jasowang@redhat.com>