Add a portalized network monitor implementation

The backend for this lives in xdg-desktop-portal,
and is in turn using GNetworkMonitor.

When network is not available in the sandbox, there is
no point in reporting accurately about the network
status outside the sandbox. Just return 'no connection'
in this case.

https://bugzilla.gnome.org/show_bug.cgi?id=768498

gio/Makefile.am

@@ -338,6 +338,27 @@ giowin32include_HEADERS = \
 
 endif
 
+xdp_dbus_built_sources = xdp-dbus.c xdp-dbus.h
+BUILT_SOURCES += $(xdp_dbus_built_sources)
+
+EXTRA_DIST += org.freedesktop.portal.NetworkMonitor.xml
+
+$(xdp_dbus_built_sources) : $(srcdir)/org.freedesktop.portal.NetworkMonitor.xml
+	$(AM_V_GEN) UNINSTALLED_GLIB_SRCDIR=$(top_srcdir) 		\
+		UNINSTALLED_GLIB_BUILDDIR=$(top_builddir) 		\
+		$(PYTHON) $(srcdir)/gdbus-2.0/codegen/gdbus-codegen.in 	\
+		--interface-prefix org.freedesktop.portal.      	\
+		--c-namespace GXdp					\
+		--generate-c-code $(builddir)/xdp-dbus			\
+		$(srcdir)/org.freedesktop.portal.NetworkMonitor.xml	\
+		$(NULL)
+
+portal_sources = \
+	gnetworkmonitorportal.c 	\
+	gnetworkmonitorportal.h		\
+	$(xdp_dbus_built_sources)	\
+	$(NULL)
+
 libgio_2_0_la_SOURCES =		\
 	gappinfo.c 		\
 	gappinfoprivate.h	\
@@ -494,6 +515,7 @@ libgio_2_0_la_SOURCES =		\
 	$(settings_sources) 	\
 	$(gdbus_sources) 	\
 	$(local_sources) 	\
+	$(portal_sources)	\
 	$(NULL)
 
 EXTRA_DIST += strinfo.c