separate allowedips from routing for multipath

[Arvid Picciani <aep@exys.org>]

Hey,

i'm considering using wireguard for a system where there can be
multiple routes to an ip.

The nearest solution i can think of is constantly changing the peer
AllowedIps from userspace and load a large list of routes into it. But
the challenge is that this is used for both routing decisions AND
policy decisions.

let's say we have 3 machines A1, A2, B and a machine that moves around V

V is currently connected via layer2 at A1,
B has V in AllowedIps for peer A1, so that any packet for V is routed to A1

now we connect V to A2 instead
we need to move the AllowedIps entry from A1 to A2 so that a packet
for V is routed to A2
old packets still arriving FROM V through A1 are now dropped

This wouldnt be an issue if AllowedIps could be separated from the
routing decision somehow.

I could have a wg interface per peer so i can do the routing using
regular linux tools, but wg doesnt like reusing the same port for
multiple wg endpoints. We'll eventually run out of ports.

I suppose port reuse is intentionally not allowed?

thanks
Arvid