MT#60558 invoke max subscribers/group license check only on POST

* max subscribers/group license check is invoked only on POST
  to enable clients to modify existing entries even if the threshold
  is reached.

Change-Id: I858b42ada5c95c179f901e43837b15358027011b

lib/NGCP/Panel/Utils/Subscriber.pm

@@ -367,6 +367,7 @@ sub prepare_resource {
         }
     }
 
+    if ($c->req->method eq 'POST') {
         my $license_max_subscribers = $c->license_max_subscribers;
         my $current_subscribers_count = $c->license_current_subscribers;
         if ($license_max_subscribers >= 0 && $current_subscribers_count >= $license_max_subscribers) {
@@ -398,6 +399,7 @@ sub prepare_resource {
             );
             return;
         }
+    }
 
     my $customer = &$getcustomer_code($resource->{customer_id});
     return unless($customer);