Consistently use ssl_handshake_start and ssl_set_handshake_header.

Some of the messages did the computation manually which would bite us if we
tried to transplant them between DTLS and TLS. More importantly, it precludes
moving the handshake hash computation from ssl_do_write to
ssl_set_handshake_header.

Change-Id: I9d400deb0720e62cb1ab905242eb0679ad650a46
Reviewed-on: https://boringssl-review.googlesource.com/2600
Reviewed-by: Adam Langley <agl@google.com>
2 files changed