get TSI_OPENSSL_ALPN_SUPPORT from env?

[soun...@gmail.com]

hi guys:

I want my server support NPN for early Android release, I'm using Python server and Android Client.

Looks like the old version does not support TLS 1.2, so we want to downgrade to NPN.

I saw the code if TSI_OPENSSL_ALPN_SUPPORT is zero, then will try to use NPN, but I can't set outside.

Could we just use gpc_getenv to load this TSI_OPENSSL_ALPN_SUPPORT instead of hard code?

[Nathaniel Manista]

(Discussion will continue in this issue.)

-Nathaniel