Merge pull request #23070 from poettering/devnum-split

basic: some devnum handling tweaks and refactorings

diff --cc src/libsystemd/sd-device/sd-device.c
index fb50a688b080b5fcea4db8ee476d728a125acf4c,22f16b9edc10193fc9b9380b969ddad4a4d0d577..bbd990bdb4b6a6accfcde49c51c77c08ed6e73fe
--- 1/src/libsystemd/sd-device/sd-device.c
--- 2/src/libsystemd/sd-device/sd-device.c
+++ b/src/libsystemd/sd-device/sd-device.c
@@@ -12,8 -12,8 +12,9 @@@
  #include "device-internal.h"
  #include "device-private.h"
  #include "device-util.h"
+ #include "devnum-util.h"
  #include "dirent-util.h"
 +#include "env-util.h"
  #include "fd-util.h"
  #include "fileio.h"
  #include "format-util.h"