Summary:
If zero copy starts out enabled on a unencrypted connection, disable
it when the SSL handshake begins. Otherwise, AsyncSocket will receive send
notifications for buffers that it did not pre-register.

Reviewed By: yfeldblum

Differential Revision: D27145232

fbshipit-source-id: f07d006d095e1e6839eb2f4adb07d7c284786572