conn,wintun: use unsafe.Slice instead of unsafeSlice

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tun/wintun/session_windows.go

@@ -67,7 +67,7 @@ func (session Session) ReceivePacket() (packet []byte, err error) {
 		err = e1
 		return
 	}
-	unsafeSlice(unsafe.Pointer(&packet), unsafe.Pointer(r0), int(packetSize))
+	packet = unsafe.Slice((*byte)(unsafe.Pointer(r0)), packetSize)
 	return
 }
 
@@ -81,28 +81,10 @@ func (session Session) AllocateSendPacket(packetSize int) (packet []byte, err er
 		err = e1
 		return
 	}
-	unsafeSlice(unsafe.Pointer(&packet), unsafe.Pointer(r0), int(packetSize))
+	packet = unsafe.Slice((*byte)(unsafe.Pointer(r0)), packetSize)
 	return
 }
 
 func (session Session) SendPacket(packet []byte) {
 	syscall.Syscall(procWintunSendPacket.Addr(), 2, session.handle, uintptr(unsafe.Pointer(&packet[0])), 0)
 }
-
-// unsafeSlice updates the slice slicePtr to be a slice
-// referencing the provided data with its length & capacity set to
-// lenCap.
-//
-// TODO: when Go 1.16 or Go 1.17 is the minimum supported version,
-// update callers to use unsafe.Slice instead of this.
-func unsafeSlice(slicePtr, data unsafe.Pointer, lenCap int) {
-	type sliceHeader struct {
-		Data unsafe.Pointer
-		Len  int
-		Cap  int
-	}
-	h := (*sliceHeader)(slicePtr)
-	h.Data = data
-	h.Len = lenCap
-	h.Cap = lenCap
-}