sky2: reduce default transmit ring

Reduce the size of the driver transmit ring to reduce latency
and allow qdisc to do better rate control.  Also make it
obvious what the minimum transmit ring allowed is and why.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/sky2.c

@@ -65,9 +65,9 @@
 #define RX_DEF_PENDING		RX_MAX_PENDING
 
 #define TX_RING_SIZE		512
-#define TX_DEF_PENDING		(TX_RING_SIZE - 1)
-#define TX_MIN_PENDING		64
+#define TX_DEF_PENDING		128
 #define MAX_SKB_TX_LE		(4 + (sizeof(dma_addr_t)/sizeof(u32))*MAX_SKB_FRAGS)
+#define TX_MIN_PENDING		(MAX_SKB_TX_LE+1)
 
 #define STATUS_RING_SIZE	2048	/* 2 ports * (TX + 2*RX) */
 #define STATUS_LE_BYTES		(STATUS_RING_SIZE*sizeof(struct sky2_status_le))