simplify content storage in packed packets

It's not necessary to store both the packetBuffer and the slice
containing the raw data in the packet.

send_queue_test.go

@@ -15,14 +15,11 @@ var _ = Describe("Send Queue", func() {
 		q = newSendQueue(c)
 	})
 
-	getPacket := func(b []byte) *packedPacket {
+	getPacket := func(b []byte) *packetBuffer {
 		buf := getPacketBuffer()
-		buf.Slice = buf.Slice[:len(b)]
-		copy(buf.Slice, b)
-		return &packedPacket{
-			buffer: buf,
-			raw:    buf.Slice,
-		}
+		buf.Data = buf.Data[:len(b)]
+		copy(buf.Data, b)
+		return buf
 	}
 
 	It("sends a packet", func() {
@@ -30,7 +27,7 @@ var _ = Describe("Send Queue", func() {
 		q.Send(p)
 
 		written := make(chan struct{})
-		c.EXPECT().Write(p.raw).Do(func([]byte) { close(written) })
+		c.EXPECT().Write([]byte("foobar")).Do(func([]byte) { close(written) })
 		done := make(chan struct{})
 		go func() {
 			defer GinkgoRecover()