fees: return current block height in estimateSmartFee

src/policy/fees/block_policy_estimator.cpp

@@ -875,6 +875,7 @@ CFeeRate CBlockPolicyEstimator::estimateSmartFee(int confTarget, FeeCalculation
     if (feeCalc) {
         feeCalc->desiredTarget = confTarget;
         feeCalc->returnedTarget = confTarget;
+        feeCalc->best_height = nBestSeenHeight;
     }
 
     double median = -1;

src/policy/fees/block_policy_estimator.h

@@ -95,6 +95,7 @@ struct FeeCalculation
     FeeReason reason = FeeReason::NONE;
     int desiredTarget = 0;
     int returnedTarget = 0;
+    unsigned int best_height{0};
 };
 
 /** \class CBlockPolicyEstimator