Fix SecGroupQuotaTest in case of unlimited quota

If project has unlimited default SG qouta (-1) test incorrectly
processing negative value.

Related-PROD: PRODX-8495
Change-Id: I62bb9fe1941cfa9c8800da99ddb9bda5a6cda5d4
diff --git a/neutron_tempest_plugin/api/test_security_groups.py b/neutron_tempest_plugin/api/test_security_groups.py
index afce414..2bbaeb8 100644
--- a/neutron_tempest_plugin/api/test_security_groups.py
+++ b/neutron_tempest_plugin/api/test_security_groups.py
@@ -133,6 +133,9 @@
     def _create_max_allowed_sg_amount(self):
         sg_amount = self._get_sg_amount()
         sg_quota = self._get_sg_quota()
+        if sg_quota == -1:
+            self._set_sg_quota(sg_amount + 1)
+            sg_quota = self._get_sg_quota()
         sg_to_create = sg_quota - sg_amount
         self._create_security_groups(sg_to_create)