[network-manager-sstp: 1/2] Let Fedora 28 compile the code.

[Eivind Næss <eivnaes src gnome org>]

commit 1ebe22baa3b771d1901bf1e9d3257a8a09565e33
Author: Eivind Næss <eivnaes yahoo com>
Date:   Sun Jun 13 10:52:01 2021 -0700

    Let Fedora 28 compile the code.

 shared/nm-default.h | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/shared/nm-default.h b/shared/nm-default.h
index 85d6114..58c329e 100644
--- a/shared/nm-default.h
+++ b/shared/nm-default.h
@@ -67,6 +67,7 @@
 #include <nm-setting-connection.h>
 #include <nm-setting-8021x.h>
 #include <nm-setting-ip4-config.h>
+#include <nm-setting-ip6-config.h>
 #include <nm-setting-vpn.h>
 #include <nm-utils.h>
 #include <nm-vpn-plugin-ui-interface.h>
@@ -103,6 +104,10 @@
 
 #endif /* NM_NETWORKMANAGER_COMPILATION_WITH_LIBNM_UTIL */
 
+#ifndef NM_SETTING_IP6_CONFIG_METHOD_DISABLED   /* Defined in NM >= 1.20 */
+#define NM_SETTING_IP6_CONFIG_METHOD_DISABLED "disabled"
+#endif
+
 /*****************************************************************************/
 
 #if (NETWORKMANAGER_COMPILATION) & NM_NETWORKMANAGER_COMPILATION_LIB_EDITOR