refactor(config): address post-approval review cleanups

Address three follow-up review comments after the initial approvals:

- xxo1shine (Args.java:345): drop the unused `config` parameter from
  `applyRateLimiterConfig`; it was a leftover from the pre-refactor path
  that used `getRateLimiterFromConfig(config)`.
- 317787106 (NodeConfig.java:387): remove the `disconnectNumberFactor`
  bean field and its reference.conf default — no code in this repo or
  in develop reads it; purely synthetic dead weight introduced by this
  PR. The other 7 keys listed by the reviewer are kept (actively used,
  legacy aliases, or public API surface); see review reply for per-key
  rationale.
- 317787106 (Args.java:1146): switch `== null` to
  `StringUtils.isEmpty(...)` on the `externalIp()` fallback guard. Not
  a behaviour change in the current architecture (no CLI flag or other
  code writes `PARAMETER.nodeExternalIp` before this point, so it can
  only be null here), but makes the intent consistent with the
  `isEmpty` checks already used on lines 1145 and 1149.

Author: vividctrlalt

common/src/main/java/org/tron/core/config/args/NodeConfig.java

@@ -88,7 +88,6 @@ public class NodeConfig {
   private boolean allowShieldedTransactionApi = true;
   private double activeConnectFactor = 0.1;
   private double connectFactor = 0.6;
-  private double disconnectNumberFactor = 0.4;
   // Legacy alias `maxActiveNodesWithSameIp` has no bean field: we only peek at it via
   // section.hasPath() below. Keeping it field-less means reference.conf doesn't have to
   // ship a default that would otherwise mask the modern `maxConnectionsWithSameIp` key.

common/src/main/resources/reference.conf

@@ -235,7 +235,6 @@ node {
   maxFastForwardNum = 4
   activeConnectFactor = 0.1
   connectFactor = 0.6
-  disconnectNumberFactor = 0.4
   # Legacy alias `maxActiveNodesWithSameIp` is still accepted from user config
   # (see NodeConfig alias-fallback) but is intentionally NOT defaulted here —
   # shipping it in reference.conf would always mask the modern `maxConnectionsWithSameIp`.

framework/src/main/java/org/tron/core/config/args/Args.java

@@ -342,7 +342,7 @@ private static void applyMiscConfig(MiscConfig mc) {
    * HTTP/RPC rate limiter lists still use getRateLimiterFromConfig() for
    * conversion to RateLimiterInitialization business objects.
    */
-  private static void applyRateLimiterConfig(RateLimiterConfig rl, Config config) {
+  private static void applyRateLimiterConfig(RateLimiterConfig rl) {
     PARAMETER.rateLimiterGlobalQps = rl.getGlobal().getQps();
     PARAMETER.rateLimiterGlobalIpQps = rl.getGlobal().getIp().getQps();
     PARAMETER.rateLimiterGlobalApiQps = rl.getGlobal().getApi().getQps();
@@ -779,7 +779,7 @@ public static void applyConfigParams(
 
     // Rate limiter config: bind from config.conf "rate.limiter" section
     rateLimiterConfig = RateLimiterConfig.fromConfig(config);
-    applyRateLimiterConfig(rateLimiterConfig, config);
+    applyRateLimiterConfig(rateLimiterConfig);
 
     // Node backup: from NodeConfig bean
     applyNodeBackupConfig(nodeConfig);
@@ -1143,7 +1143,7 @@ private static void logEmptyError(String arg) {
   private static void externalIp(NodeConfig nodeConfig) {
     String externalIp = nodeConfig.getDiscoveryExternalIp();
     if (StringUtils.isEmpty(externalIp)) {
-      if (PARAMETER.nodeExternalIp == null) {
+      if (StringUtils.isEmpty(PARAMETER.nodeExternalIp)) {
         logger.info("External IP wasn't set, using ipv4 from libp2p");
         PARAMETER.nodeExternalIp = PARAMETER.p2pConfig.getIp();
         if (StringUtils.isEmpty(PARAMETER.nodeExternalIp)) {