device: get rid of nonce routine

This moves to a simple queue with no routine processing it, to reduce
scheduler pressure.

This splits latency in half!

benchmark                  old ns/op     new ns/op     delta
BenchmarkThroughput-16     2394          2364          -1.25%
BenchmarkLatency-16        259652        120810        -53.47%

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/queueconstants_ios.go

@@ -10,6 +10,7 @@ package device
 /* Fit within memory limits for iOS's Network Extension API, which has stricter requirements */
 
 const (
+	QueueStagedSize            = 128
 	QueueOutboundSize          = 1024
 	QueueInboundSize           = 1024
 	QueueHandshakeSize         = 1024