This introduces another knob into SSL_AEAD_CTX to omit the version from the ad
parameter. It also allows us to fold a few more SSL3_ENC_METHOD hooks together.
Change-Id: I6540d410d4722f734093554fb434dab6e5217d4f
Reviewed-on: https://boringssl-review.googlesource.com/2698
Reviewed-by: Adam Langley <agl@google.com>
