message: Reduce trace level of "Got ALPN: None" message
  Occasionally handy but also noisy. Let's drop it to trace level.
diff: @@ -19,7 +19,7 @@ use crate::secrets::SecretHolder;
  use crate::ssl::{self, PRBool};
  use crate::time::{PRTime, Time};
  -use neqo_common::{matches, qdebug, qinfo, qwarn};
  +use neqo_common::{matches, qdebug, qinfo, qtrace, qwarn};
  use std::cell::RefCell;
  use std::convert::{TryFrom, TryInto};
  use std::ffi::CString;
  @@ -79,7 +79,7 @@ fn get_alpn(fd: *mut ssl::PRFileDesc, pre: bool) -> Res<Option<String>> {
  }
  _ => None,
  };
  - qinfo!([format!("{:p}", fd)], "got ALPN {:?}", alpn);
  + qtrace!([format!("{:p}", fd)], "got ALPN {:?}", alpn);
  Ok(alpn)
  }
  