TUN-6999: cloudflared should attempt other edge addresses before falling back on protocol

This PR does two things:
It changes how we fallback to a lower protocol: The current state
is to try connecting with a protocol. If it fails, fall back to a
lower protocol. And try connecting with that and so on. With this PR,
if we fail to connect with a protocol, we will try to connect to other
edge addresses first. Only if we fail to connect to those will we
fall back to a lower protocol.
It fixes a behaviour where if we fail to connect to an edge addr,
we keep re-trying the same address over and over again.
This PR now switches between edge addresses on subsequent connecton attempts.
Note that through these switches, it still respects the backoff time.
(We are connecting to a different edge, but this helps to not bombard an edge
address with connect requests if a particular edge addresses stops working).

cmd/cloudflared/tunnel/cmd.go

@@ -612,6 +612,12 @@ func tunnelFlags(shouldHide bool) []cli.Flag {
 			Value:  5,
 			Hidden: true,
 		}),
+		altsrc.NewIntFlag(&cli.IntFlag{
+			Name:   "max-edge-addr-retries",
+			Usage:  "Maximum number of times to retry on edge addrs before falling back to a lower protocol",
+			Value:  8,
+			Hidden: true,
+		}),
 		// Note TUN-3758 , we use Int because UInt is not supported with altsrc
 		altsrc.NewIntFlag(&cli.IntFlag{
 			Name:    "retries",

cmd/cloudflared/tunnel/configuration.go

@@ -376,15 +376,16 @@ func prepareTunnelConfig(
 		Observer:        observer,
 		ReportedVersion: info.Version(),
 		// Note TUN-3758 , we use Int because UInt is not supported with altsrc
-		Retries:          uint(c.Int("retries")),
-		RunFromTerminal:  isRunningFromTerminal(),
-		NamedTunnel:      namedTunnel,
-		ClassicTunnel:    classicTunnel,
-		MuxerConfig:      muxerConfig,
-		ProtocolSelector: protocolSelector,
-		EdgeTLSConfigs:   edgeTLSConfigs,
-		NeedPQ:           needPQ,
-		PQKexIdx:         pqKexIdx,
+		Retries:            uint(c.Int("retries")),
+		RunFromTerminal:    isRunningFromTerminal(),
+		NamedTunnel:        namedTunnel,
+		ClassicTunnel:      classicTunnel,
+		MuxerConfig:        muxerConfig,
+		ProtocolSelector:   protocolSelector,
+		EdgeTLSConfigs:     edgeTLSConfigs,
+		NeedPQ:             needPQ,
+		PQKexIdx:           pqKexIdx,
+		MaxEdgeAddrRetries: uint8(c.Int("max-edge-addr-retries")),
 	}
 	packetConfig, err := newPacketConfig(c, log)
 	if err != nil {