nwfilter: Add missing goto err_exit in error path

https://bugzilla.redhat.com/show_bug.cgi?id=1071095

Add a missing goto err_exit in the error path where an unsupported
value is assigned to the CTRL_IP_LEARNING key.
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>

src/nwfilter/nwfilter_gentech_driver.c

@@ -732,6 +732,7 @@ virNWFilterInstantiate(const unsigned char *vmuuid ATTRIBUTE_UNUSED,
                                _("filter '%s' "
                                  "learning value '%s' invalid."),
                                filter->name, learning);
+                goto err_exit;
             }
         } else
              goto err_unresolvable_vars;