The map[key.NodePublic][]netip.Prefix that flows from route manager
commits to WireGuard device syncs has subtle semantics (a nil value
means the peer was removed or no longer contributes any prefixes)
that were documented on routemanager.Result.AllowedIPs and then
re-documented, or not, at each signature that passed it along. Give
it a named type, PeersWithRouteChanges, and document the nil
semantics once on it.
Updates #12542
Change-Id: I2566361a5331eb11b2b70a5bcdb497cc20ee561d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
87c0d36942