Convert the renegotiation extension to the new system.

This change also switches the behaviour of the client. Previously the
client would send the SCSV rather than the extension, but now it'll only
do that for SSLv3 connections.

Change-Id: I67a04b8abbef2234747c0dac450458deb6b0cd0a
Reviewed-on: https://boringssl-review.googlesource.com/5143
Reviewed-by: Adam Langley <agl@google.com>
14 files changed