kern/53255: NetBSD32 compat fails to process secondary CMSG option

[roy%marples.name@localhost]

>Number:         53255
>Category:       kern
>Synopsis:       NetBSD32 compat fails to process secondary CMSG option
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu May 03 12:30:00 +0000 2018
>Originator:     Roy Marples
>Release:        NetBSD-8
>Organization:
>Environment:
$ uname -a
NetBSD erlite.marples.name 8.99.14 NetBSD 8.99.14 (ERLITE) #4: Fri Apr 27 14:33:44 BST 2018  roy%netbsd.marples.name@localhost:/home/roy/obj/src-evbmips/sys/arch/evbmips/compile/ERLITE evbmips
>Description:
Setup a Router Soliciation message.
Set the first CMSG option to set a hoplimit of 255 (this is valid)
Set the second CMSG option to set the outbound interface index of 255 (this is invalid)

On ERLITE sendmsg(2) reports success.
On AMD64 sendmsg(2) reports no such device.
>How-To-Repeat:
Test case here:
http://www.netbsd.org/~roy/cmsg.c
>Fix: