any is vfs.nfsrv.nfs_privport=0 by default

[Rick Macklem]

> vfs.nfsrv.nfs_privport controls wither or not NFS enforces the
> traditional RPC semantics that require that requests come from
> "privileged" ports. By default this check is disabled. Hardening
> guides typically suggest this be enabled, usually via the rc.conf knob
> nfs_reserved_port_only=YES.
> 
> I'm trying to find a good reason why the default is the way it is.
> Digging around in the source tree it appears that the rc.conf setting
> has been that way since either /etc/rc.conf or /etc/defaults/rc.conf
> has
> been in the tree.
> 
> I do not consider the fact that the security provided is weak at best
> to
> be a good reason to disable it. I suspect support for PC-NFS or
> something like that may be the reason, but if that's the case it
> really
> doesn't make any sense.
> 
Two comments:
1 - RFC3530 (NFSv4) specifically states that reserved port #s cannot be
    required.
    --> If you change the defaults, it will be different for NFSv4 than
        NFSv2,3. Not incorrect, but a little weird.
2 - It was probably disabled by default so that clients wouldn't run out
    of reserved ports when doing lotsa mounts.

But, I don't care what the default is for NFSv2,3, rick