conf-parser: turn three bool function params into a flags fields

This makes things more readable and fixes some issues with incorrect
flag propagation between the various flavours of config_parse().

src/core/load-dropin.c

@@ -154,12 +154,11 @@ int unit_load_dropin(Unit *u) {
                         return log_oom();
         }
 
-        STRV_FOREACH(f, u->dropin_paths) {
-                config_parse(u->id, *f, NULL,
-                             UNIT_VTABLE(u)->sections,
-                             config_item_perf_lookup, load_fragment_gperf_lookup,
-                             false, false, false, u);
-        }
+        STRV_FOREACH(f, u->dropin_paths)
+                (void) config_parse(u->id, *f, NULL,
+                                    UNIT_VTABLE(u)->sections,
+                                    config_item_perf_lookup, load_fragment_gperf_lookup,
+                                    0, u);
 
         u->dropin_mtime = now(CLOCK_REALTIME);
 

src/core/load-fragment.c

@@ -4450,7 +4450,7 @@ static int load_from_path(Unit *u, const char *path) {
                 r = config_parse(u->id, filename, f,
                                  UNIT_VTABLE(u)->sections,
                                  config_item_perf_lookup, load_fragment_gperf_lookup,
-                                 false, true, false, u);
+                                 CONFIG_PARSE_ALLOW_INCLUDE, u);
                 if (r < 0)
                         return r;
         }

src/core/main.c

@@ -768,7 +768,7 @@ static int parse_config_file(void) {
                 CONF_PATHS_NULSTR("systemd/system.conf.d") :
                 CONF_PATHS_NULSTR("systemd/user.conf.d");
 
-        config_parse_many_nulstr(fn, conf_dirs_nulstr, "Manager\0", config_item_table_lookup, items, false, NULL);
+        (void) config_parse_many_nulstr(fn, conf_dirs_nulstr, "Manager\0", config_item_table_lookup, items, CONFIG_PARSE_WARN, NULL);
 
         /* Traditionally "0" was used to turn off the default unit timeouts. Fix this up so that we used USEC_INFINITY
          * like everywhere else. */