Data race in streamImpl: concurrent access to LastByteSent/FirstByteSent

[NikoMalik]

Description:

When running tests with the -race flag, gosec detects data races in streamImpl methods LastByteSent() and FirstByteSent(). The race occurs due to concurrent reads (in sender's multiCB callback) and writes (in StreamsPool.Acquire()) on the shared fields of streamImpl.

Read at 0x00c0006166e0 by goroutine 27:
  ...streamImpl.LastByteSent()
  ...sender.multiCB.Call() at sender.go:308

Previous write at 0x00c0006166e0 by goroutine 22:
  ...StreamsPool.Acquire() at pool.go:51

and similarly for FirstByteSent().