Fix: don't hardcode alpn protocol byte size (openssl) (#14769)

For some reason OpenSSL used to negotiate the protocol by itself,
without invoking the select callback, or maybe it didn't respect the
total bytesize when processing the alpn string.

That changed in the 3.0.14 and other bugfix releases of OpenSSL, which
exposed the bug.

Author: ysbaddaden

src/openssl/ssl/context.cr

@@ -178,7 +178,7 @@ abstract class OpenSSL::SSL::Context
       {% if LibSSL.has_method?(:ssl_ctx_set_alpn_select_cb) %}
         alpn_cb = ->(ssl : LibSSL::SSL, o : LibC::Char**, olen : LibC::Char*, i : LibC::Char*, ilen : LibC::Int, data : Void*) {
           proto = Box(Bytes).unbox(data)
-          ret = LibSSL.ssl_select_next_proto(o, olen, proto, 2, i, ilen)
+          ret = LibSSL.ssl_select_next_proto(o, olen, proto, proto.size, i, ilen)
           if ret != LibSSL::OPENSSL_NPN_NEGOTIATED
             LibSSL::SSL_TLSEXT_ERR_NOACK
           else