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/Ethernet.java b/src/main/java/net/onrc/onos/core/packet/Ethernet.java
index 19e7c70..ef088db 100644
--- a/src/main/java/net/onrc/onos/core/packet/Ethernet.java
+++ b/src/main/java/net/onrc/onos/core/packet/Ethernet.java
@@ -57,7 +57,7 @@
     protected boolean pad = false;
 
     /**
-     * By default, set Ethernet to untagged
+     * By default, set Ethernet to untagged.
      */
     public Ethernet() {
         super();
@@ -323,7 +323,7 @@
     }
 
     /**
-     * Convert a long MAC address to a byte array
+     * Convert a long MAC address to a byte array.
      *
      * @param macAddress
      * @return the bytes of the mac address
@@ -478,7 +478,7 @@
         } else if (pkt instanceof BPDU) {
             sb.append("\nbpdu packet");
         } else {
-            sb.append("\nunknwon packet");
+            sb.append("\nunknown packet");
         }
 
         return sb.toString();