Correct and update mapping of D_AGC values

Ref issue#1775 (part 1)
Corrected mapping of D_AGC values to currently enumerated AGC set. Will separately provide alternate mapping, if required, in backends that require it.

rigs/icom/icom_defs.h

@@ -232,10 +232,13 @@
 /*
  * Set AGC (S_FUNC_AGC) data
  */
-#define D_AGC_FAST	0x00
-#define D_AGC_MID	0x01
-#define D_AGC_SLOW	0x02
-#define D_AGC_SUPERFAST	0x03 /* IC746 pro */
+#define D_AGC_OFF	0x00
+#define D_AGC_SUPERFAST	0x01 //was 0x03 /* IC746 pro */
+#define D_AGC_FAST	0x02 //was 0x00
+#define D_AGC_SLOW	0x03 //was 0x02
+#define D_AGC_USER	0x04
+#define D_AGC_MID	0x05 //was 0x01
+#define D_AGC_AUTO	0x06
 
 /*
  * Set antenna (C_SET_ANT) subcommands