Enable checkstyle Javadoc Comment Style rule

Turn on the Javadoc Comment Style rule and fix
any violations that come up.  This is related to
requiring javadoc description comments to end
with a '.'

Change-Id: I19cf1b9f00d3040987e0b4c8b39461e2e0ad66b5
diff --git a/src/main/java/net/onrc/onos/core/packet/ICMP.java b/src/main/java/net/onrc/onos/core/packet/ICMP.java
index eb42f96..c1a0883 100644
--- a/src/main/java/net/onrc/onos/core/packet/ICMP.java
+++ b/src/main/java/net/onrc/onos/core/packet/ICMP.java
@@ -20,7 +20,7 @@
 import java.nio.ByteBuffer;
 
 /**
- * Implements ICMP packet format
+ * Implements ICMP packet format.
  *
  * @author shudong.zhou@bigswitch.com
  */