Deprecate NetUtil.isIp4Word()

NetUtil.isIp4Word() was meant to be a utility method of other public
methods in NetUtil, and was published mistakenly.

common/src/main/java/io/netty/util/NetUtil.java

@@ -554,6 +554,10 @@ public final class NetUtil {
         return true;
     }
 
+    /**
+     * @deprecated Do not use; published by mistake.
+     */
+    @Deprecated
     public static boolean isValidIp4Word(String word) {
         char c;
         if (word.length() < 1 || word.length() > 3) {