supplicant: make sure we remove the right interface

It shouldn't ever happen that two interface objects for the same
network interface are active at the same time, but make sure we
yell if it does.

src/supplicant-manager/nm-supplicant-manager.c

@@ -88,8 +88,13 @@ nm_supplicant_manager_iface_release (NMSupplicantManager *self,
 	g_return_if_fail (NM_IS_SUPPLICANT_MANAGER (self));
 	g_return_if_fail (NM_IS_SUPPLICANT_INTERFACE (iface));
 
+	ifname = nm_supplicant_interface_get_ifname (iface);
+	g_assert (ifname);
+
 	priv = NM_SUPPLICANT_MANAGER_GET_PRIVATE (self);
 
+	g_return_if_fail (g_hash_table_lookup (priv->ifaces, ifname) == iface);
+
 	/* Ask wpa_supplicant to remove this interface */
 	op = nm_supplicant_interface_get_object_path (iface);
 	if (priv->running && priv->proxy && op) {
@@ -98,8 +103,6 @@ nm_supplicant_manager_iface_release (NMSupplicantManager *self,
 			                        G_TYPE_INVALID);
 	}
 
-	ifname = nm_supplicant_interface_get_ifname (iface);
-	g_assert (ifname);
 	g_hash_table_remove (priv->ifaces, ifname);
 }