Identify a live route by prefix and peer (closes #55)

A peer has at most one route per prefix, but both live route tables were
unique on prefix, origin AS and peer. A peer that changed a prefix's origin
AS left its old route behind, and a withdrawal sent in the same message as
announcements was given their origin AS and missed the withdrawn route.

Both tables are now unique on prefix and peer. An announcement replaces the
peer's row for the prefix, origin AS included; a withdrawal deletes it
without looking at an origin AS. The route counts and prefix distribution
kept in memory stay exact, for IPv4 and IPv6.

Model: opus-5-5

internal/database/counts_test.go

@@ -128,7 +128,7 @@ func TestLiveCountsTrackWritesInRealtime(t *testing.T) {
 
 	// A withdrawal removes one route.
 	if err := db.DeleteLiveRouteBatch([]LiveRouteDeletion{
-		{Prefix: "203.0.113.0/24", OriginASN: 64501, PeerIP: "192.0.2.1", IPVersion: ipVersionV4},
+		{Prefix: "203.0.113.0/24", PeerIP: "192.0.2.1", IPVersion: ipVersionV4},
 	}); err != nil {
 		t.Fatalf("DeleteLiveRouteBatch: %v", err)
 	}
@@ -327,13 +327,11 @@ func announceRoutes(db *Database, batch bool, routes []*LiveRoute) error {
 }
 
 // withdrawRoutes removes routes in one DeleteLiveRouteBatch, or with one
-// DeleteLiveRoute each. It names each route by prefix and peer only, with no
-// origin ASN, as a withdrawal from the feed does when its message carries no AS
-// path.
+// DeleteLiveRoute each.
 func withdrawRoutes(db *Database, batch bool, routes []*LiveRoute) error {
 	if !batch {
 		for _, route := range routes {
-			if err := db.DeleteLiveRoute(route.Prefix, 0, route.PeerIP); err != nil {
+			if err := db.DeleteLiveRoute(route.Prefix, route.PeerIP); err != nil {
 				return err
 			}
 		}