Fix InternalAttribute.equals

Motivation:

InternalAttribute doesn't extend Attribute, but its equals only returns true when it compares with an Attribute. So it will return false when comparing with itself.

Modifications:

Make sure InternalAttribute return false for non InternalAttribute objects.

Result:

InternalAttribute's equals works correctly.

codec-http/src/main/java/io/netty/handler/codec/http/multipart/InternalAttribute.java

@@ -79,10 +79,10 @@ public int hashCode() {
 
     @Override
     public boolean equals(Object o) {
-        if (!(o instanceof Attribute)) {
+        if (!(o instanceof InternalAttribute)) {
             return false;
         }
-        Attribute attribute = (Attribute) o;
+        InternalAttribute attribute = (InternalAttribute) o;
         return getName().equalsIgnoreCase(attribute.getName());
     }