RequestGroup -> 64
RequestGroup -> 64

Summary: This is a more reasonable number. There's plenty of room on the stack.

Reviewed By: shodoco

Differential Revision: D32171870

fbshipit-source-id: 44c0a4ac640689fb8bc73045f78fafd48bc25876

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst