[network-manager-sstp] Adding the include directory for src/ as it now includes headers.

[Eivind Næss <eivnaes src gnome org>]

commit 0deadecf66480cd0ca3743288b8e5a51d777b635
Author: Eivind Næss <eivnaes yahoo com>
Date:   Sun Jun 13 11:23:30 2021 -0700

    Adding the include directory for src/ as it now includes headers.

 Makefile.am | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/Makefile.am b/Makefile.am
index 8f87655..44bf9da 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -47,6 +47,7 @@ src_cppflags = \
        -DG_LOG_DOMAIN=\"nm-sstp\" \
        -DNETWORKMANAGER_COMPILATION=NM_NETWORKMANAGER_COMPILATION_DEFAULT \
        -I$(builddir)/src \
+       -I$(top_srcdir)/src \
        -I$(top_srcdir)/shared \
        $(GLIB_CFLAGS) \
        $(LIBNM_CFLAGS) \