DataFlash: Update logging of EKF2 primary core index

Changes made in response to review comments

libraries/DataFlash/DataFlash.h

@@ -461,7 +461,7 @@ struct PACKED log_NKF4 {
     uint8_t timeouts;
     uint16_t solution;
     uint16_t gps;
-    uint8_t primary;
+    int8_t primary;
 };
 
 struct PACKED log_EKF5 {
@@ -832,7 +832,7 @@ Format characters in the format string for binary log messages
     { LOG_NKF3_MSG, sizeof(log_NKF3), \
       "NKF3","Qcccccchhhcc","TimeUS,IVN,IVE,IVD,IPN,IPE,IPD,IMX,IMY,IMZ,IYAW,IVT" }, \
     { LOG_NKF4_MSG, sizeof(log_NKF4), \
-      "NKF4","QcccccfbbBBHHB","TimeUS,SV,SP,SH,SM,SVT,errRP,OFN,OFE,FS,TS,SS,GPS,PI" }, \
+      "NKF4","QcccccfbbBBHHb","TimeUS,SV,SP,SH,SM,SVT,errRP,OFN,OFE,FS,TS,SS,GPS,PI" }, \
     { LOG_NKF5_MSG, sizeof(log_EKF5), \
       "NKF5","QBhhhcccCC","TimeUS,normInnov,FIX,FIY,AFI,HAGL,offset,RI,meaRng,errHAGL" }, \
     { LOG_TERRAIN_MSG, sizeof(log_TERRAIN), \

libraries/DataFlash/LogFile.cpp

@@ -1367,8 +1367,7 @@ void DataFlash_Class::Log_Write_EKF2(AP_AHRS_NavEKF &ahrs, bool optFlowEnabled)
     ahrs.get_NavEKF2().getFilterGpsStatus(gpsStatus);
     float tiltError;
     ahrs.get_NavEKF2().getTiltError(tiltError);
-    uint8_t primaryIndex;
-    ahrs.get_NavEKF2().getPrimaryCoreIndex(primaryIndex);
+    uint8_t primaryIndex = ahrs.get_NavEKF2().getPrimaryCoreIndex();
     struct log_NKF4 pkt4 = {
         LOG_PACKET_HEADER_INIT(LOG_NKF4_MSG),
         time_us : hal.scheduler->micros64(),
@@ -1384,7 +1383,7 @@ void DataFlash_Class::Log_Write_EKF2(AP_AHRS_NavEKF &ahrs, bool optFlowEnabled)
         timeouts : (uint8_t)(timeoutStatus),
         solution : (uint16_t)(solutionStatus.value),
         gps : (uint16_t)(gpsStatus.value),
-        primary : (uint8_t)primaryIndex
+        primary : (int8_t)primaryIndex
     };
     WriteBlock(&pkt4, sizeof(pkt4));