Allow to change config file (sub)directory

This allows the `xrdp` part of the path `/etc/xrdp` where config files
are placed to be customizable. This change is useful when trying the
stable version and the devel version alternately.

sesman/chansrv/Makefile.am

@@ -4,7 +4,7 @@ EXTRA_DIST = \
   wave-format-server.txt
 
 AM_CPPFLAGS = \
-  -DXRDP_CFG_PATH=\"${sysconfdir}/xrdp\" \
+  -DXRDP_CFG_PATH=\"${sysconfdir}/${sysconfsubdir}\" \
   -DXRDP_SBIN_PATH=\"${sbindir}\" \
   -DXRDP_SHARE_PATH=\"${datadir}/xrdp\" \
   -DXRDP_PID_PATH=\"${localstatedir}/run\" \