explore the no-masking extension

[vinniefalco]

https://www.ietf.org/archive/id/draft-damjanovic-websockets-nomasking-00.html

[ashtum]

Related, #2987

[xim]

If there's interest, I could try to explore making a PR. A (not veri rigorous) benchmark on a (somewhat high-powered) embedded device showed an increased throughput of 20-25% after removing masking.