net: dsa: mv88e6xxx: Longer timeout for PTP TX timestamp

For slow processors using bit-banging MDIO, 20ms can be too short a
timeout when waiting for the transmit timestamp to become
available. Double it to 40ms.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/hwtstamp.c

@@ -65,7 +65,7 @@ static int mv88e6xxx_ptp_read(struct mv88e6xxx_chip *chip, int addr,
  * within 1ms. Software may enounter delays due to MDIO contention, so
  * the timeout is set accordingly.
  */
-#define TX_TSTAMP_TIMEOUT	msecs_to_jiffies(20)
+#define TX_TSTAMP_TIMEOUT	msecs_to_jiffies(40)
 
 int mv88e6xxx_get_ts_info(struct dsa_switch *ds, int port,
 			  struct ethtool_ts_info *info)