basic/set: let set_put_strdup() create the set with string hash ops

If we're using a set with _put_strdup(), most of the time we want to use
string hash ops on the set, and free the strings when done. This defines
the appropriate a new string_hash_ops_free structure to automatically free
the keys when removing the set, and makes set_put_strdup() and set_put_strdupv()
instantiate the set with those hash ops.

hashmap_put_strdup() was already doing something similar.

(It is OK to instantiate the set earlier, possibly with a different hash ops
structure. set_put_strdup() will then use the existing set. It is also OK
to call set_free_free() instead of set_free() on a set with
string_hash_ops_free, the effect is the same, we're just overriding the
override of the cleanup function.)

No functional change intended.

src/udev/udevadm-trigger.c

@@ -23,7 +23,7 @@
 static bool arg_verbose = false;
 static bool arg_dry_run = false;
 
-static int exec_list(sd_device_enumerator *e, const char *action, Set *settle_set) {
+static int exec_list(sd_device_enumerator *e, const char *action, Set **settle_set) {
         sd_device *d;
         int r, ret = 0;
 
@@ -172,7 +172,7 @@ int trigger_main(int argc, char *argv[], void *userdata) {
         _cleanup_(sd_device_enumerator_unrefp) sd_device_enumerator *e = NULL;
         _cleanup_(sd_device_monitor_unrefp) sd_device_monitor *m = NULL;
         _cleanup_(sd_event_unrefp) sd_event *event = NULL;
-        _cleanup_set_free_free_ Set *settle_set = NULL;
+        _cleanup_set_free_ Set *settle_set = NULL;
         usec_t ping_timeout_usec = 5 * USEC_PER_SEC;
         bool settle = false, ping = false;
         int c, r;
@@ -342,7 +342,7 @@ int trigger_main(int argc, char *argv[], void *userdata) {
         }
 
         if (settle) {
-                settle_set = set_new(&string_hash_ops);
+                settle_set = set_new(&string_hash_ops_free);
                 if (!settle_set)
                         return log_oom();
 
@@ -377,7 +377,8 @@ int trigger_main(int argc, char *argv[], void *userdata) {
         default:
                 assert_not_reached("Unknown device type");
         }
-        r = exec_list(e, action, settle_set);
+
+        r = exec_list(e, action, settle ? &settle_set : NULL);
         if (r < 0)
                 return r;