fix: do not request ALPN on standard ports and when using STARTTLS

Apparently some providers fail TLS connection
with "no_application_protocol" alert
even when requesting "imap" protocol for IMAP connection
and "smtp" protocol for SMTP connection.

Fixes <https://github.com/deltachat/deltachat-core-rust/issues/5892>.

src/net.rs

@@ -114,7 +114,7 @@ pub(crate) async fn connect_tls_inner(
     addr: SocketAddr,
     host: &str,
     strict_tls: bool,
-    alpn: &str,
+    alpn: &[&str],
 ) -> Result<TlsStream<Pin<Box<TimeoutStream<TcpStream>>>>> {
     let tcp_stream = connect_tcp_inner(addr).await?;
     let tls_stream = wrap_tls(strict_tls, host, alpn, tcp_stream).await?;