AP_Logger: add 1e-9 log multiplyer

libraries/AP_Logger/LogStructure.h

@@ -101,6 +101,7 @@ const struct MultiplierStructure log_Multipliers[] = {
     { 'E', 1e-5 },
     { 'F', 1e-6 },
     { 'G', 1e-7 },
+    { 'I', 1e-9 },
 // <leave a gap here, just in case....>
     { '!', 3.6 }, // (ampere*second => milliampere*hour) and (km/h => m/s)
     { '/', 3600 }, // (ampere*second => ampere*hour)

libraries/AP_Logger/README.md

@@ -100,5 +100,6 @@ tl;dr a GCS shouldn't/mustn't infer any scaling from the unit name
 | 'E' | 1e-5 ||
 | 'F' | 1e-6 ||
 | 'G' | 1e-7 ||
+| 'I' | 1e-9 ||
 | '!' | 3.6 | (milliampere \* hour => ampere \* second) and (km/h => m/s)|
 | '/' | 3600 | (ampere \* hour => ampere \* second)|