Data race in serverPool.start

[b00ris]

System information

Geth version: 1.7.2
OS & Version: Windows/Linux/OSX
Commit hash : a5d08c8

Expected behaviour

No data races in the code.

Actual behaviour

Data race caused channels assignment after starting reading goroutine.

Steps to reproduce the behaviour

I've found this data race while running test of Status-IM project: github.com/status-im/status-go/e2e/account_test.(*TestAccountsTestSuite).TestAccountsList()

Backtrace

WARNING: DATA RACE
Read at 0x00c4200db920 by goroutine 62:
  github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les.(*serverPool).eventLoop()
      /home/b00ris/go/src/github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les/serverpool.go:281 +0x62

Previous write at 0x00c4200db920 by goroutine 32:
  github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les.(*serverPool).start()
      /home/b00ris/go/src/github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les/serverpool.go:152 +0x342
  github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les.(*LightEthereum).Start()
      /home/b00ris/go/src/github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les/backend.go:212 +0x221
  github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/node.(*Node).Start()
      /home/b00ris/go/src/github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/node/node.go:196 +0xe17

....
WARNING: DATA RACE
Read at 0x00c4200db928 by goroutine 62:
  github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les.(*serverPool).eventLoop()
      /home/b00ris/go/src/github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les/serverpool.go:314 +0x153

Previous write at 0x00c4200db928 by goroutine 32:
  github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les.(*serverPool).start()
      /home/b00ris/go/src/github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les/serverpool.go:153 +0x3aa
  github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les.(*LightEthereum).Start()
      /home/b00ris/go/src/github.com/status-im/status-go/vendor/github.com/ethereum/go-ethereum/les/backend.go:212 +0x221