pkg/devicemapper: comment nitpicks

1. devmapper_wrapper_{,no_}deferred_remove.go:
Comments about LibraryDeferredRemovalSupport were very totally
misleading to me. This thing has nothing to do with either static
or dynamic linking (but with build tags). Fix the comment accordingly.

2. devmapper.go:
Reveal the source of those magic device* constants.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

pkg/devicemapper/devmapper.go

@@ -13,6 +13,7 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+// Same as DM_DEVICE_* enum values from libdevmapper.h
 const (
 	deviceCreate TaskType = iota
 	deviceReload

pkg/devicemapper/devmapper_wrapper_deferred_remove.go

@@ -8,7 +8,7 @@ package devicemapper
 */
 import "C"
 
-// LibraryDeferredRemovalSupport is supported when statically linked.
+// LibraryDeferredRemovalSupport tells if the feature is enabled in the build
 const LibraryDeferredRemovalSupport = true
 
 func dmTaskDeferredRemoveFct(task *cdmTask) int {

pkg/devicemapper/devmapper_wrapper_no_deferred_remove.go

@@ -2,7 +2,7 @@
 
 package devicemapper
 
-// LibraryDeferredRemovalSupport is not supported when statically linked.
+// LibraryDeferredRemovalSupport tells if the feature is enabled in the build
 const LibraryDeferredRemovalSupport = false
 
 func dmTaskDeferredRemoveFct(task *cdmTask) int {