tools: allow to limit xenstore features via guest config

Add a guest config parameter "xenstore_feature_mask" allowing to limit
the Xenstore features the guest can see and use. This can be needed in
order to allow migrating a guest to a host running a Xenstore version
providing less features than the source host.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Acked-by: Nick Rosbrook <enr0n@ubuntu.com> # tools/golang
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

tools/xl/xl_parse.c

@@ -1409,6 +1409,9 @@ void parse_config_data(const char *config_source,
     if (!xlu_cfg_get_string (config, "pool", &buf, 0))
         xlu_cfg_replace_string(config, "pool", &c_info->pool_name, 0);
 
+    if (!xlu_cfg_get_long (config, "xenstore_feature_mask", &l, 0))
+        b_info->xenstore_feature_mask = l;
+
     libxl_domain_build_info_init_type(b_info, c_info->type);
 
     if (b_info->type == LIBXL_DOMAIN_TYPE_PVH) {