20000 nested coroutines require 20 GB of virtual address space.
Only nest 1000 of them so that the test (only enabled with
"-m perf" on the command line) runs on 32-bit machines too.

Cc: qemu-stable@nongnu.org
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>