Use the record-layer buffer for sniffing V2ClientHellos.

I'm not sure why I made a separate one. (Not quite how the V2ClientHello
code will look in the buffer-free API yet. Probably the future
refactored SSL_HANDSHAKE gadget will need separate entry points to
consume a handshake message or V2ClientHello and the driver deals with
framing.)

This also means that ssl3_setup_read_buffer is never called external to
ssl3_read_n.

BUG=468889

Change-Id: I872f1188270968bf53ee9d0488a761c772a11e9e
Reviewed-on: https://boringssl-review.googlesource.com/5713
Reviewed-by: Adam Langley <agl@google.com>
3 files changed