make links private in ddspan

Author: amarziali

dd-java-agent/testing/src/main/groovy/datadog/trace/agent/test/asserts/LinksAssert.groovy

@@ -14,7 +14,7 @@ class LinksAssert {
   private final Set<AgentSpanLink> assertedLinks = []
 
   private LinksAssert(DDSpan span) {
-    this.links = span.links // this is class protected but for the moment groovy can access it
+    this.links = span.links // this is class private but for the moment groovy can access it
   }
 
   static void assertLinks(DDSpan span,

dd-trace-core/src/main/java/datadog/trace/core/DDSpan.java

@@ -107,7 +107,7 @@ static DDSpan create(
    */
   private volatile int longRunningVersion = 0;
 
-  protected final List<AgentSpanLink> links;
+  private final List<AgentSpanLink> links;
 
   /**
    * Spans should be constructed using the builder, not by calling the constructor directly.