logind: introduce macro for the last session class condition check

For all checks regarding the properties of sessoin classes we have
SESSION_CLASS_CAN_XYZ() style macros. Except for one. Convert that one
too.

src/login/logind-dbus.c

@@ -1835,7 +1835,7 @@ static int have_multiple_sessions(
         /* Check for other users' sessions. Greeter sessions do not
          * count, and non-login sessions do not count either. */
         HASHMAP_FOREACH(session, m->sessions)
-                if (IN_SET(session->class, SESSION_USER, SESSION_USER_EARLY) &&
+                if (SESSION_CLASS_IS_INHIBITOR_LIKE(session->class) &&
                     session->user->user_record->uid != uid)
                         return true;
 

src/login/logind-session.h

@@ -65,6 +65,9 @@ typedef enum SessionClass {
 /* Which session classes allow changing session types */
 #define SESSION_CLASS_CAN_CHANGE_TYPE(class) (IN_SET((class), SESSION_USER, SESSION_USER_EARLY, SESSION_GREETER, SESSION_LOCK_SCREEN))
 
+/* Which session classes are taken into acccount when deciding whether shutdown shall be allowed if other users are logged in */
+#define SESSION_CLASS_IS_INHIBITOR_LIKE(class) IN_SET((class), SESSION_USER, SESSION_USER_EARLY)
+
 typedef enum SessionType {
         SESSION_UNSPECIFIED,
         SESSION_TTY,