Until now BGP connections have only been established
when the space server has initiated the connection to
the peer.

It's best practice for both BGP speakers to be able to
connect to one another, lowering recovery time.

This patch changes the reverse path filtering of the labicolo VLAN
to take place in the prerouting hook, using the kernel routing
table, and removes the need to maintain a static prefix list.

Labicolo routes are exported to the kernel routing table by BIRD,
hence it should be sufficient to only have prefix lists there.

This change has been tested, and it's only possible to spoof
fellow labicolo members address space (same as before).

Now that we use communities, we don't need this prefix filter
anymore, only the per-customer prefix filters.

We only announce a prefix, if we have recieved it from a customer
connection or if we originate it our self.

This way we avoid announcing prefixes matching the earlier used,
prefix list if we haven't recieved it via the customer connection.
This is important for multi-homed labicolo customers.

Assign large communities on prefix import.

Later we can then use the community, to decide if we should
announce it to our peers.

This patch prepares us for adopting Large BGP Communities (RFC 8092).

Basic format of Large BGP Communities:
  <uint32_t asn>:<uint32_t function>:<uint32_t value>

We use function 1 for storing prefix type (or relation).

We then assign a value to transit, peering, customer and originated
prefixes.

Large BGP Communities
http://largebgpcommunities.net/
https://tools.ietf.org/html/rfc8092
https://tools.ietf.org/html/rfc8195

This protects us amount otherthings against 3rd parties
resetting the TCP connection underneat our BGP sessions.

This has been enabled in both ends, and this
_MUST_ remain enabled, otherwise these sessions
will go down.

If this needs to be disabled for some reason
then it must be coordinated with Fiberby.

RFC 5082 - The Generalized TTL Security Mechanism
https://datatracker.ietf.org/doc/html/rfc5082

The prefix was only routeable on the intern network, not the whole
internet, as it was not added in local_prefix_v6.
The 2a0e:8f02:f034::/48 is attached to my ASN, AS211153

Commit message fixed up by Esmil

Commit message and nftables rule fixed up by Esmil