coroutine: trim down nesting level in perf_nesting test

coroutine: trim down nesting level in perf_nesting test

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: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 027003152f4cf21952f9282b4487daf3fdd372ba)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>