Fix sentWaitChan usage

1 job for async_send.0 in 10 minutes and 55 seconds
Status Job ID Name Coverage
  Test
failed #2925
test-client

00:10:55

10.1%
 
Name Stage Failure
failed
test-client Test
--- PASS: TestTimerQueueRemove (3.01s)
timer_queue_test.go:103: Sent 10 messages
timer_queue_test.go:114: Popped 5 messages
PASS
coverage: 10.1% of statements in ./...
ok github.com/katzenpost/client/session 5.063s coverage: 10.1% of statements in ./...
? github.com/katzenpost/client/utils [no test files]
FAIL
ERROR: Job failed: exit code 1