core/mount: support "systemctl clean" for mount units

src/basic/unit-def.c

@@ -136,7 +136,8 @@ static const char* const mount_state_table[_MOUNT_STATE_MAX] = {
         [MOUNT_REMOUNTING_SIGKILL] = "remounting-sigkill",
         [MOUNT_UNMOUNTING_SIGTERM] = "unmounting-sigterm",
         [MOUNT_UNMOUNTING_SIGKILL] = "unmounting-sigkill",
-        [MOUNT_FAILED] = "failed"
+        [MOUNT_FAILED] = "failed",
+        [MOUNT_CLEANING] = "cleaning",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(mount_state, MountState);

src/basic/unit-def.h

@@ -79,6 +79,7 @@ typedef enum MountState {
         MOUNT_UNMOUNTING_SIGTERM,
         MOUNT_UNMOUNTING_SIGKILL,
         MOUNT_FAILED,
+        MOUNT_CLEANING,
         _MOUNT_STATE_MAX,
         _MOUNT_STATE_INVALID = -1
 } MountState;