TUN-6696: Refactor flow into funnel and close idle funnels

A funnel is an abstraction for 1 source to many destinations.
As part of this refactoring, shared logic between Darwin and Linux are moved into icmp_posix

ingress/icmp_linux_test.go

@@ -1,52 +0,0 @@
-//go:build linux
-
-package ingress
-
-import (
-	"errors"
-	"net"
-	"net/netip"
-	"testing"
-	"time"
-
-	"github.com/stretchr/testify/require"
-
-	"github.com/cloudflare/cloudflared/packet"
-)
-
-func TestCloseIdleFlow(t *testing.T) {
-	const (
-		echoID      = 19234
-		idleTimeout = time.Millisecond * 100
-	)
-	conn, err := newICMPConn(localhostIP)
-	require.NoError(t, err)
-	flow := packet.Flow{
-		Src: netip.MustParseAddr("172.16.0.1"),
-	}
-	icmpFlow := newICMPFlow(conn, &flow, echoID, &noopLogger)
-	shutdownC := make(chan struct{})
-	flowErr := make(chan error)
-	go func() {
-		flowErr <- icmpFlow.serve(shutdownC, idleTimeout)
-	}()
-
-	require.Equal(t, errFlowInactive, <-flowErr)
-}
-
-func TestCloseConnStopFlow(t *testing.T) {
-	const (
-		echoID = 19234
-	)
-	conn, err := newICMPConn(localhostIP)
-	require.NoError(t, err)
-	flow := packet.Flow{
-		Src: netip.MustParseAddr("172.16.0.1"),
-	}
-	icmpFlow := newICMPFlow(conn, &flow, echoID, &noopLogger)
-	shutdownC := make(chan struct{})
-	conn.Close()
-
-	err = icmpFlow.serve(shutdownC, defaultCloseAfterIdle)
-	require.True(t, errors.Is(err, net.ErrClosed))
-}