net: sgi: ioc3-eth: separate tx and rx ring handling

After allocation of descriptor memory is now done once in probe
handling of tx ring is completely done by ioc3_clean_tx_ring. So
we remove the remaining tx ring actions out of ioc3_alloc_rings
and ioc3_free_rings and rename it to ioc3_[alloc|free]_rx_bufs
to better describe what they are doing.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>