network: Allow compiling against NM 0.9.6

NM 0.9.7 has still not been released, even as a tarball, so allow
compiling against 0.9.6 (without certain bits of new functionality).

https://bugzilla.gnome.org/show_bug.cgi?id=691721

panels/network/connection-editor/net-connection-editor.c

@@ -582,7 +582,9 @@ typedef struct {
 static const NetConnectionType connection_types[] = {
         { N_("VPN"), nm_setting_vpn_get_type },
         { N_("Bond"), nm_setting_bond_get_type },
+#ifdef HAVE_NM_UNSTABLE
         { N_("Bridge"), nm_setting_bridge_get_type },
+#endif
         { N_("VLAN"), nm_setting_vlan_get_type }
 };
 static const NetConnectionType *vpn_connection_type = &connection_types[0];