Merge attribute handling from request and response to commen code.

packages/ipp/naturallanguage.go

@@ -16,9 +16,14 @@ func NewNaturalLanguage(name, value string) *naturalLanguage {
 	return c
 }
 
+func (c naturalLanguage) Name() string {
+	return c.name
+}
+
 func (c naturalLanguage) String() string {
 	return c.name + ":" + c.value
 }
+
 func (c *naturalLanguage) valueTag() tag {
 	return naturalLanguageValueTag
 }