net: stmmac: increase TX coalesce timer to 5ms

Commit 8fce3331 ("net: stmmac: Rework coalesce timer and fix
multi-queue races") decreased the TX coalesce timer from 40ms to 1ms.

This caused some performance regression on some target (regression was
reported at least on ipq806x) in the order of 600mbps dropping from
gigabit handling to only 200mbps.

The problem was identified in the TX timer getting armed too much time.
While this was fixed and improved in another commit, performance can be
improved even further by increasing the timer delay a bit moving from
1ms to 5ms.

The value is a good balance between battery saving by prevending too
much interrupt to be generated and permitting good performance for
internet oriented devices.
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/stmicro/stmmac/common.h

@@ -293,7 +293,7 @@ struct stmmac_safety_stats {
 #define MIN_DMA_RIWT		0x10
 #define DEF_DMA_RIWT		0xa0
 /* Tx coalesce parameters */
-#define STMMAC_COAL_TX_TIMER	1000
+#define STMMAC_COAL_TX_TIMER	5000
 #define STMMAC_MAX_COAL_TX_TICK	100000
 #define STMMAC_TX_MAX_FRAMES	256
 #define STMMAC_TX_FRAMES	25