MT#56234 get_usr_preference_rs and prov_subscriber

* get_usr_prerefence_rs is streamlined to the other
  get_*_preference_rs functions and prov_subscriber
  param is now optional there, that allows to return
  a resultset of usr preferences matching the attribute
  name.
* this fix also fixes DELETE soundset where if contract_id
  is defined, the logic tries to remove all 'contract_sound_set'
  usr_preference across all subscribers that have it assigned.

Change-Id: Ia43327c8bcf93047d29da6401cbd97bce2971578

lib/NGCP/Panel/Utils/Preferences.pm

@@ -2472,14 +2472,14 @@ sub get_usr_preference_rs {
     my $prov_subscriber = $params{prov_subscriber};
     my $schema = $params{schema} // $c->model('DB');
 
-    return unless $prov_subscriber;
-
     my $preference = $schema->resultset('voip_preferences')->find({
         attribute => $attribute,
         usr_pref => 1,
     });
     return unless $preference;
 
+    return $preference->voip_usr_preferences unless $prov_subscriber;
+
     return $preference->voip_usr_preferences->search_rs({
         subscriber_id => $prov_subscriber->id,
     });