Add static all-zero IP address

Change-Id: I235e88b710ca2867bc381a04f579aa9da0199227
diff --git a/utils/misc/src/main/java/org/onlab/packet/Ip4Address.java b/utils/misc/src/main/java/org/onlab/packet/Ip4Address.java
index 36b6f81..5047271 100644
--- a/utils/misc/src/main/java/org/onlab/packet/Ip4Address.java
+++ b/utils/misc/src/main/java/org/onlab/packet/Ip4Address.java
@@ -33,6 +33,11 @@
     public static final int BIT_LENGTH = IpAddress.INET_BIT_LENGTH;
 
     /**
+     * All-zero unspecified IPv4 address.
+     */
+    public static final Ip4Address ZERO = Ip4Address.valueOf("0.0.0.0");
+
+    /**
      * Constructor for given IP address version and address octets.
      *
      * @param value the IP address value stored in network byte order
diff --git a/utils/misc/src/main/java/org/onlab/packet/Ip6Address.java b/utils/misc/src/main/java/org/onlab/packet/Ip6Address.java
index 02a1e15..046920a 100644
--- a/utils/misc/src/main/java/org/onlab/packet/Ip6Address.java
+++ b/utils/misc/src/main/java/org/onlab/packet/Ip6Address.java
@@ -32,6 +32,11 @@
     public static final int BIT_LENGTH = IpAddress.INET6_BIT_LENGTH;
 
     /**
+     * All-zero unspecified IPv6 address.
+     */
+    public static final Ip6Address ZERO = Ip6Address.valueOf("::");
+
+    /**
      * Constructor for given IP address version and address octets.
      *
      * @param value the IP address value stored in network byte order