add check around read guardrail to avoid enum-set allocation similarly to write path

Author: Matt Byrd

src/java/org/apache/cassandra/cql3/statements/SelectStatement.java

@@ -369,7 +369,8 @@ public ResultMessage.Rows execute(QueryState state, QueryOptions options, Dispat
         checkNotNull(cl, "Invalid empty consistency level");
 
         cl.validateForRead();
-        Guardrails.readConsistencyLevels.guard(EnumSet.of(cl), state.getClientState());
+        if Guardrails.readConsistencyLevels.enabled(clientState)
+            Guardrails.readConsistencyLevels.guard(EnumSet.of(cl), state.getClientState());
 
         long nowInSec = options.getNowInSeconds(state);
         int userLimit = getLimit(options);