vl.c: numa_add(): Validate nodeid before using it

Without this check, QEMU will corrupt memory if a too-large nodeid is
provided in the command-line. e.g.:

  -numa node,mem=...,cpus=...,nodeid=65

This changes nodenr to unsigned long long, to avoid integer conversion
issues when converting the strtoull() result to int.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
