Merge attribute handling from request and response to commen code.

packages/ipp/charsetvalue.go

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