Add UDP source IP into golang dialer https connection for Edgeview

- have seen on certain EVE devices, even walk through various ports, the
  UDP source IP address used stuck on one particular IP address, and it
  then failed on DNS query and failed Edgeview connection.
- change retry connection backoff after walking through all the intfs to
  speed up the initial connection time

Signed-off-by: Naiming Shen <naiming@zededa.com>

pkg/edgeview/src/websocket.go

@@ -1,10 +1,11 @@
-// Copyright (c) 2021 Zededa, Inc.
+// Copyright (c) 2021-2005 Zededa, Inc.
 // SPDX-License-Identifier: Apache-2.0
 
 package main
 
 import (
 	"bytes"
+	"context"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/json"
@@ -89,6 +90,13 @@ func setupWebC(hostname, token string, u url.URL, isServer bool) bool {
 		useProxy++
 		// walk through default route intfs if exist, and try also without specifying the source
 		// if we know the index it worked previously before disconnect, try that first
+		// For the source IP, we on EVE device, relies on the policy routing to route the
+		// IP packets to the correct outbound interface. For a normal Linux host, this may
+		// not be available, or it needs to be implemented on the host which runs Edgeview.
+		// The below for loop, only gets the interfaces pointed to by default IP route,
+		// and using the Interface IP address as the source IP for the TLS connection, it walks
+		// through all the interfaces on this list, plus one more without using the source IP,
+		// in the case the controller IP route is statically configured in the routing table.
 		for idx := len(intfSrcs) - 1; idx >= -1; idx-- {
 			if websIndex != invalidIndex && websIndex < len(intfSrcs) {
 				idx = websIndex
@@ -136,11 +144,13 @@ func setupWebC(hostname, token string, u url.URL, isServer bool) bool {
 				}
 				return true
 			}
-			retry++
 			if !isServer && retry > 1 {
 				return false
 			}
 		}
+		// do exponential backoff after walking through all the interfaces
+		// to speed up the connection retrial
+		retry++
 	}
 }
 
@@ -175,7 +185,21 @@ func tlsDial(isServer bool, pIP string, pport int, src []net.IP, idx int) (*webs
 		dialer.Proxy = http.ProxyURL(proxyURL)
 	}
 	if idx >= 0 && len(src) > 0 && idx < len(src) {
-		dialer.NetDialContext = (&net.Dialer{LocalAddr: &net.TCPAddr{IP: src[idx]}}).DialContext
+		srcSelected := src[idx]
+		localAddr := &net.TCPAddr{IP: srcSelected}
+		netDialer := &net.Dialer{
+			LocalAddr: localAddr,
+			Resolver: &net.Resolver{
+				PreferGo: true,
+				Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+					d := net.Dialer{
+						LocalAddr: &net.UDPAddr{IP: srcSelected},
+					}
+					return d.DialContext(ctx, network, address)
+				},
+			},
+		}
+		dialer.NetDialContext = netDialer.DialContext
 	}
 
 	return dialer, nil