Reduce default number of blocks to check at startup

Github-Pull: #8611
Rebased-From: 203f2121be

src/main.h

@@ -192,7 +192,7 @@ extern uint64_t nPruneTarget;
 /** Block files containing a block-height within MIN_BLOCKS_TO_KEEP of chainActive.Tip() will not be pruned. */
 static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
 
-static const signed int DEFAULT_CHECKBLOCKS = MIN_BLOCKS_TO_KEEP;
+static const signed int DEFAULT_CHECKBLOCKS = 6;
 static const unsigned int DEFAULT_CHECKLEVEL = 3;
 
 // Require that user allocate at least 550MB for block & undo files (blk???.dat and rev???.dat)