Re-use THeaderProtocol on serve requests to support legacy clients
Re-use THeaderProtocol on serve requests to support legacy clients

Summary: D2353161 introduced performance fixes for timeout handling, unfortunately breaking support for legacy FRAMED clients. This diff restores that functionality and documents it better.

Test Plan: fbconfig wormhole/tools && fbmake dev && fbmake runtests_dev; also, manual `bunnylol fb303 $HOST $PORT` works again for asyncio servers.

Reviewed By: dgp@fb.com

Subscribers: alandau, yfeldblum

FB internal diff: D2453471

Tasks: 8116353

Signature: t1:2453471:1442516254:576ada30ef7cf8b228602a70b0690a76a35e8d1d

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