ScheduledFutureTask#delayNanos doesn't return negative values [1], but it looks like the Delayed allows negative values to represent "the delay has elapsed". Do we always need to limit to positive values, and can we remove some computation here?

It looks like NioEventLoop may be depending upon the non-negative values [2].

[1] https://github.com/netty/netty/blob/4.1/common/src/main/java/io/netty/util/concurrent/ScheduledFutureTask.java#L85-L91
[2] https://github.com/netty/netty/blob/4.1/transport/src/main/java/io/netty/channel/nio/NioEventLoop.java#L732