dns/dnsmessage: remove unnecessary []byte conversions

Change-Id: I1a5445584d582e8ace9d336a83e39d3a55d6ab45
GitHub-Last-Rev: 283a809ae9
GitHub-Pull-Request: golang/net#147
Reviewed-on: https://go-review.googlesource.com/c/net/+/426634
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

dns/dnsmessage/message.go

@@ -1899,11 +1899,11 @@ type Name struct {
 
 // NewName creates a new Name from a string.
 func NewName(name string) (Name, error) {
-	if len([]byte(name)) > nameLen {
+	if len(name) > nameLen {
 		return Name{}, errCalcLen
 	}
 	n := Name{Length: uint8(len(name))}
-	copy(n.Data[:], []byte(name))
+	copy(n.Data[:], name)
 	return n, nil
 }