Use a different socks port number for channel ''.

Channel '' apparently happens for local builds, and we don't want it
to step on the toes of release builds.

fix #14592

This is a stop-gap measure until we use an OS-chosen socks port
number or a local socket as in #12936.

Auditors: @diracdeltas @bsclifton

Test Plan:
1. Launch a local development build of Brave.
2. Laucnh a release build of Brave.
3. Confirm that Tor works in both.

app/channel.js

@@ -67,7 +67,6 @@ exports.getTorSocksProxy = () => {
   let portno
   switch (channel) {
     case 'dev':
-    case '':
     default:
       portno = 9250
       break
@@ -80,6 +79,9 @@ exports.getTorSocksProxy = () => {
     case 'developer':
       portno = 9280
       break
+    case '':
+      portno = 9290
+      break
   }
   return `socks5://127.0.0.1:${portno}`
 }