igb: Add comment

Add explanatory comment to avoid confusion when a pointer is set
to the second word of an array instead of the customary cast of a
pointer to the beginning of the array.
Signed-off-by: NGreg Rose <gregory.v.rose@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/igb/igb_main.c

@@ -4974,6 +4974,10 @@ static void igb_vf_reset_msg(struct igb_adapter *adapter, u32 vf)
 
 static int igb_set_vf_mac_addr(struct igb_adapter *adapter, u32 *msg, int vf)
 {
+	/*
+	 * The VF MAC Address is stored in a packed array of bytes
+	 * starting at the second 32 bit word of the msg array
+	 */
 	unsigned char *addr = (char *)&msg[1];
 	int err = -1;