Akamai example is broken on negotiated ALPN

[GlenDC]

The akamai example (https://github.com/hyperium/h2/blob/master/examples/akamai.rs) is broken on the assert_eq!(Some(ALPN_H2.as_bytes()), negotiated_protocol) statement.

Can easily be "fixed" by moving it to example.com instead, but given that a lot of tests make use of akamai I imagine you have good reasons for wanting to use their server.

Seems the ALPN is not returned in the location supported by rustls. It does contain ALPN data in 1.3 encryption, but didn't dive deep enough to see if that indeed contains h2 confirmation or not. Forcing it to tls 1.2 also doesn't change anything. example.com server does return the h2 ALPN back as selection.

I don't mind submitting a patch for it, but didn't know what you prefer here. Whatever the case be, currently the example fails.