References: bsc#1167608
unbound limits for max_event_channels
1023 is too low for a three digit value of vcpus
it is difficult to make the value depend on the number of vcpus
adding devices at runtime also needs event channels
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -224,7 +224,7 @@ int libxl__domain_build_info_setdefault(
             b_info->iomem[i].gfn = b_info->iomem[i].start;
 
     if (!b_info->event_channels)
-        b_info->event_channels = 1023;
+        b_info->event_channels = -1U;
 
     libxl__arch_domain_build_info_setdefault(gc, b_info);
     libxl_defbool_setdefault(&b_info->dm_restrict, false);