net: via-rhine: add BQL support

Add Byte Queue Limits (BQL) support to via-rhine driver.

[edumazet] tweaked patch and changed TX_RING_SIZE from 16 to 64

Signed-off-by: Tino Reichardt <milky-kernel@mcmilk.de>
Tested-by: Jamie Gloudon <jamie.gloudon@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>