hyperv: Configure IPv6 when setting up VF failover

The default VF-up script moves IPv4 configuration from the synthetic
interface to a failover lagg, but leaves IPv6 unconfigured on the lagg.
Adding

hyperv: Configure IPv6 when setting up VF failover

The default VF-up script moves IPv4 configuration from the synthetic
interface to a failover lagg, but leaves IPv6 unconfigured on the lagg.
Adding the synthetic interface as a member can remove its IPv6 addresses,
so deleting the remaining member addresses is not sufficient.

Stop accepting router advertisements on the synthetic interface before
adding it to the lagg. Leave its link-local address and IPv6 enable state
in place for lagg's address, prefix and default-router cleanup, then disable
IPv6 and explicitly remove any remaining addresses. This also covers
members without a link-local address or with IPv6 already disabled.

Replay the synthetic interface's IPv6 rc.conf configuration on the lagg,
including aliases, prefix-derived addresses and legacy configuration names.
Remap the variables in a subshell and reuse network.subr's IPv6 helpers.
For SLAAC, solicit fresh router advertisements rather than copying learned
addresses as permanent ones. Configure IPv6 independently of the IPv4
DHCP/static choice, and leave existing laggs alone on repeated invocation.
Custom DHCPv6 clients and interface-scoped static routes still require the
per-interface setup hook.

Fixes: c68595695679 ("hyperv: Add VF bringup scripts and devd rules.")
MFC after: 2 weeks
Sponsored by: BBOX.io

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hyperv: Bound IPv4 address removal when configuring VF failover

The VF-up script repeatedly deletes the first IPv4 address from hn until
ifconfig fails. Netlink-based ifconfig returns success when

hyperv: Bound IPv4 address removal when configuring VF failover

The VF-up script repeatedly deletes the first IPv4 address from hn until
ifconfig fails. Netlink-based ifconfig returns success when no address
remains, so the script can loop forever and block subsequent devd work.

Use ipv4_down() from the already-sourced network.subr to enumerate the
addresses and delete each explicitly. This also handles multiple
addresses without relying on the exit status of an empty deletion. The
behavior depends on ifconfig, not the VF hardware, so no device-specific
fallback is needed.

Fixes: c68595695679 ("hyperv: Add VF bringup scripts and devd rules.")
MFC after: 2 weeks
Sponsored by: BBOX.io

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hyperv: Add VF bringup scripts and devd rules.

How network VF works with hn(4) on Hyper-V in non-transparent mode:

- Each network VF has a cooresponding hn(4).
- The network VF and the it's cooresp

hyperv: Add VF bringup scripts and devd rules.

How network VF works with hn(4) on Hyper-V in non-transparent mode:

- Each network VF has a cooresponding hn(4).
- The network VF and the it's cooresponding hn(4) have the same hardware
address.
- Once the network VF is up, e.g. ifconfig VF up:
o All of the transmission should go through the network VF.
o Most of the reception goes through the network VF.
o Small amount of reception may go through the cooresponding hn(4).
This reception will happen, even if the the cooresponding hn(4) is
down. The cooresponding hn(4) will change the reception interface
to the network VF, so that network layer and application layer will
be tricked into thinking that these packets were received by the
network VF.
o The cooresponding hn(4) pretends the physical link is down.
- Once the network VF is down or detached:
o All of the transmission should go through the cooresponding hn(4).
o All of the reception goes through the cooresponding hn(4).
o The cooresponding hn(4) fallbacks to the original physical link
detection logic.

All these features are mainly used to help live migration, during which
the network VF will be detached, while the network communication to the
VM must not be cut off. In order to reach this level of live migration
transparency, we use failover mode lagg(4) with the network VF and the
cooresponding hn(4) attached to it.

To ease user configuration for both network VF and non-network VF, the
lagg(4) will be created by the following rules, and the configuration
of the cooresponding hn(4) will be applied to the lagg(4) automatically.

Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D11635

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