Use a cleaner mechanism to test whether an IP address or prefix
is IPv4 or IPv6.

Change-Id: Ia88f76be87a30573a50eeeedb78d98713ac1ae27
diff --git a/core/net/src/main/java/org/onosproject/net/host/impl/HostMonitor.java b/core/net/src/main/java/org/onosproject/net/host/impl/HostMonitor.java
index 8e6d16a..fe7d77f 100644
--- a/core/net/src/main/java/org/onosproject/net/host/impl/HostMonitor.java
+++ b/core/net/src/main/java/org/onosproject/net/host/impl/HostMonitor.java
@@ -21,7 +21,6 @@
 import org.onlab.packet.Ethernet;
 import org.onlab.packet.ICMP6;
 import org.onlab.packet.IpAddress;
-import org.onlab.packet.Ip4Address;
 import org.onlab.packet.IPv6;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
@@ -205,7 +204,7 @@
                                  VlanId vlan) {
         Ethernet probePacket = null;
 
-        if (targetIp.version() == Ip4Address.VERSION) {
+        if (targetIp.isIp4()) {
             // IPv4: Use ARP
             probePacket = buildArpRequest(targetIp, sourceIp, sourceMac,
                                           vlan);