rpcserver: Modify getnetworkhashps -1 blocks logic.

Now that the target difficulty is calculated every block as opposed to
on an interval, the logic in the getnetworkhashps RPC that treated a
negative number of blocks as a signal to calculate back to the most
recent difficulty change no longer makes sense.

Thus, this updates the getnetworkhashps RPC to ignore negative values
so that the default number of blocks is used instead.

It also updates the RPC server help description accordingly to remove
mention of the previous behavior.

internal/rpcserver/rpcserver.go

@@ -2599,27 +2599,15 @@ func handleGetNetworkHashPS(_ context.Context, s *Server, cmd interface{}) (inte
 		endHeight = best.Height
 	}
 
-	// Calculate the number of blocks per retarget interval based on the
-	// chain parameters.
-	params := s.cfg.ChainParams
-	blocksPerRetarget := int64(params.TargetTimespan / params.TargetTimePerBlock)
-
-	// Calculate the starting block height based on the passed number of
-	// blocks.  When the passed value is negative, use the last block the
-	// difficulty changed as the starting height.  Also make sure the
+	// Calculate the starting block height based on the passed number of blocks.
+	// When the passed value is negative, use the default.  Also, make sure the
 	// starting height is not before the beginning of the chain.
-
 	numBlocks := int64(120)
-	if c.Blocks != nil {
+	if c.Blocks != nil && *c.Blocks >= 0 {
 		numBlocks = int64(*c.Blocks)
 	}
 
-	var startHeight int64
-	if numBlocks <= 0 {
-		startHeight = endHeight - ((endHeight % blocksPerRetarget) + 1)
-	} else {
-		startHeight = endHeight - numBlocks
-	}
+	startHeight := endHeight - numBlocks
 	if startHeight < 0 {
 		startHeight = 0
 	}

internal/rpcserver/rpcserverhandlers_test.go

@@ -4567,11 +4567,9 @@ func TestHandleGetNetworkHashPS(t *testing.T) {
 	networkHashPSResult := int64(2014899978133500709)
 
 	testRPCServerHandler(t, []rpcTest{{
-		name:    "handleGetNetworkHashPS: ok",
-		handler: handleGetNetworkHashPS,
-		cmd: &types.GetNetworkHashPSCmd{
-			Blocks: dcrjson.Int(0),
-		},
+		name:      "handleGetNetworkHashPS: ok",
+		handler:   handleGetNetworkHashPS,
+		cmd:       &types.GetNetworkHashPSCmd{},
 		mockChain: mc(),
 		result:    networkHashPSResult,
 	}, {

internal/rpcserver/rpcserverhelp.go

@@ -512,7 +512,7 @@ var helpDescsEnUS = map[string]string{
 
 	// GetNetworkHashPSCmd help.
 	"getnetworkhashps--synopsis": "Returns the estimated network hashes per second for the block heights provided by the parameters.",
-	"getnetworkhashps-blocks":    "The number of blocks, or -1 for blocks since last difficulty change",
+	"getnetworkhashps-blocks":    "The number of blocks or -1 for the default number of blocks",
 	"getnetworkhashps-height":    "Perform estimate ending with this height or -1 for current best chain block height",
 	"getnetworkhashps--result0":  "Estimated hashes per second",