miner: don't re-apply default Options value if argument is unset

ApplyArgsManOptions does not need to set default values for missing
arguments, these are already defined in the BlockAssembler::Options.

This commit changes the interface of ApplyArgsManOptions(). If
ApplyArgsManOptions() is called again after a option is changed,
this option will no longer be reset to the default value.

There is no observed behaviour change due to how
ApplyArgsManOptions() is currently used, and the new interface is
consistent with e.g. ValidationCacheSizes and MemPoolLimits.

Author: stickies-v

src/node/miner.cpp

@@ -74,13 +74,9 @@ BlockAssembler::BlockAssembler(Chainstate& chainstate, const CTxMemPool* mempool
 void ApplyArgsManOptions(const ArgsManager& args, BlockAssembler::Options& options)
 {
     // Block resource limits
-    // If -blockmaxweight is not given, limit to DEFAULT_BLOCK_MAX_WEIGHT
-    options.nBlockMaxWeight = args.GetIntArg("-blockmaxweight", DEFAULT_BLOCK_MAX_WEIGHT);
-    if (args.IsArgSet("-blockmintxfee")) {
-        std::optional<CAmount> parsed = ParseMoney(args.GetArg("-blockmintxfee", ""));
-        options.blockMinFeeRate = CFeeRate{parsed.value_or(DEFAULT_BLOCK_MIN_TX_FEE)};
-    } else {
-        options.blockMinFeeRate = CFeeRate{DEFAULT_BLOCK_MIN_TX_FEE};
+    options.nBlockMaxWeight = args.GetIntArg("-blockmaxweight", options.nBlockMaxWeight);
+    if (const auto blockmintxfee{args.GetArg("-blockmintxfee")}) {
+        if (const auto parsed{ParseMoney(*blockmintxfee)}) options.blockMinFeeRate = CFeeRate{*parsed};
     }
 }
 static BlockAssembler::Options ConfiguredOptions()