virnetdaemon: fix memory leak in virNetDaemonCallInhibit

virnetdaemon: fix memory leak in virNetDaemonCallInhibit

g_variant_new() returns a weak reference which can be consumed by passing
to other g_variant* functions or to g_dbus_connection_call* functions.

This make it possible to call g_variant_new() directly as argument to
the functions above. Because this might be confusing I explicitly call
g_variant_ref_sink() to make it normal reference in both
virGDBusCallMethod() and virGDBusCallMethodWithFD() so the caller is
always responsible for the data.

Reported-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>