Added methods to test whether an IP address/prefix is IPv4 or IPv6:
  IpAddress.isIp4()
  IpAddress.isIp6()
  IpPrefix.isIp4()
  IpPrefix.isIp6()

Also, added the corresponding unit tests.

Change-Id: I2b1f08501c94d61f75b15f2c6977c0349e313ebd
diff --git a/utils/misc/src/main/java/org/onlab/packet/IpAddress.java b/utils/misc/src/main/java/org/onlab/packet/IpAddress.java
index f8d9f2f..699ad47 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IpAddress.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IpAddress.java
@@ -80,6 +80,24 @@
     }
 
     /**
+     * Tests whether the IP version of this address is IPv4.
+     *
+     * @return true if the IP version of this address is IPv4, otherwise false.
+     */
+    public boolean isIp4() {
+        return (version() == Ip4Address.VERSION);
+    }
+
+    /**
+     * Tests whether the IP version of this address is IPv6.
+     *
+     * @return true if the IP version of this address is IPv6, otherwise false.
+     */
+    public boolean isIp6() {
+        return (version() == Ip6Address.VERSION);
+    }
+
+    /**
      * Gets the {@link Ip4Address} view of the IP address.
      *
      * @return the {@link Ip4Address} view of the IP address if it is IPv4,