Right whether NPN is advertised can only be configured globally on the SSL_CTX.
Rather than adding two pointers to each SSL*, add an options bit to disable it
so we may plumb in a field trial to disable NPN.
Chromium wants to be able to route a bit in to disable NPN, but it uses SSL_CTX
incorrectly and has a global one, so it can't disconnect the callback. (That
really needs to get fixed. Although it's not clear this necessarily wants to be
lifted up to SSL_CTX as far as Chromium's SSLClientSocket is concerned since
NPN doesn't interact with the session cache.)
BUG=526713
Change-Id: I49c86828b963eb341c6ea6a442557b7dfa190ed3
Reviewed-on: https://boringssl-review.googlesource.com/6351
Reviewed-by: Adam Langley <alangley@gmail.com>
091c4b9869