Use VlanId.vlanId(short) to validate the value

Also update the unit test
    - VlanId.vlanId("5000") should throw IllegalArgumentException

Change-Id: I374532080dc2a51da8f2c0a46ea92df6f8abbe56
diff --git a/utils/misc/src/main/java/org/onlab/packet/VlanId.java b/utils/misc/src/main/java/org/onlab/packet/VlanId.java
index 04b87f1..92d8a59 100644
--- a/utils/misc/src/main/java/org/onlab/packet/VlanId.java
+++ b/utils/misc/src/main/java/org/onlab/packet/VlanId.java
@@ -92,7 +92,7 @@
             return new VlanId(ANY_VALUE);
         }
         try {
-            return new VlanId(Short.parseShort(value));
+            return VlanId.vlanId(Short.parseShort(value));
         } catch (NumberFormatException e) {
             throw new IllegalArgumentException(e);
         }