numa: Reject duplicate node IDs

The same nodeid shouldn't appear multiple times in the command-line.

In addition to detecting command-line mistakes, this will fix a bug
where nb_numa_nodes may become larger than MAX_NODES (and cause
out-of-bounds access on the numa_info array).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
