[WIP] Add IPv6 NFS Root support

[bz]

Summary

A first cut at NFS Root over IPv6 support.
So far no bootp support as it is unclear how we'll
be called when doing UEFI IPv6 booting yet.
Needs investigation probably with bhyve.

To be clear, this is a work-in-progress.

Test Plan

Set a few loader variables and can see the initial TCP
packet but the NFS handle and state will not be right
if booted from a different IPv4 server initially.

boot.netif.ip6="2001:db8:7c78::2/64"
boot.netif.gateway6="0"
boot.nfsroot.server6="2001:db8:7c78::1"

[darkfiberiru_gmail.com]

Trying to understand your bootp comment in summary. Are you pointing at no support yet for https://tools.ietf.org/html/rfc5970 or that there just isn't a ipv6 option for defining boot info like bootp had?

[bz]

In D22487#491857, @darkfiberiru_gmail.com wrote:

Trying to understand your bootp comment in summary. Are you pointing at no support yet for https://tools.ietf.org/html/rfc5970 or that there just isn't a ipv6 option for defining boot info like bootp had?

I think neither yet. Just trying to figure out how all this will be passed in/on from each stage to the next; We need to get the info from efi in the loader and from there on also to the kernel, and depending on how we do that we'll need to right glue code.

I'd prefer to have bootp instead of the NFS_ROOT stuff. But we have a good mix of options (including the standalone NFS client) and until I have my test setup to work from EFI forward I've deferred a decision and am just trying to get the 2nd half sorted.

Unrelated, I think I broke IPv4 ...

[bz]

inet_pton() stroes network byte order, so lose the original (now extra)
htonl() and unbreak IPv4 support.