Motivation:

Networking software like SwiftNIO that always has explicit flushes
usually does not benefit from having TCP_NODELAY switched off. The
benefits of having it turned on are usually quite substantial and yet we
forced our users for the longest time to enable it manually.

Quite a bit of engineering time has been lost finding performance
problems and it turns out switching TCP_NODELAY on solves them
magically.

Netty has made the switch to TCP_NODELAY on by default, SwiftNIO should
follow.

Modifications:

Enable TCP_NODELAY by default.

Result:

If the user forgot to enable TCP_NODELAY, their software should now be
faster.