igb: ethtool -d reads EICR which is incorrect as it is read on clear

Ethtool -d is reading the EICR and ICR registers which is currently
clearing these registers and masking off interrupts.  To prevent this we
read the EICS and ICS equivilents as they can be read without clearing or
masking.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/igb/igb_ethtool.c

@@ -373,13 +373,17 @@ static void igb_get_regs(struct net_device *netdev,
 	regs_buff[12] = rd32(E1000_EECD);
 
 	/* Interrupt */
-	regs_buff[13] = rd32(E1000_EICR);
+	/* Reading EICS for EICR because they read the
+	 * same but EICS does not clear on read */
+	regs_buff[13] = rd32(E1000_EICS);
 	regs_buff[14] = rd32(E1000_EICS);
 	regs_buff[15] = rd32(E1000_EIMS);
 	regs_buff[16] = rd32(E1000_EIMC);
 	regs_buff[17] = rd32(E1000_EIAC);
 	regs_buff[18] = rd32(E1000_EIAM);
-	regs_buff[19] = rd32(E1000_ICR);
+	/* Reading ICS for ICR because they read the
+	 * same but ICS does not clear on read */
+	regs_buff[19] = rd32(E1000_ICS);
 	regs_buff[20] = rd32(E1000_ICS);
 	regs_buff[21] = rd32(E1000_IMS);
 	regs_buff[22] = rd32(E1000_IMC);