Always use DnsEndPoint in SocketHttpHandler's ConnectAsync (#29286) (#29303)

We had a minor optimization here, but there's a long-standing issue with Socket.ConnectAsync where it's leaving for finalization a socket when the connect with an IP address fails.  It's more important to address that issue, and using DnsEndPoint does so (it's also the code we want, anyway).

Author: stephentoub

src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs

@@ -54,9 +54,7 @@ public CertificateCallbackMapper(Func<HttpRequestMessage, X509Certificate2, X509
                 saea.Initialize(cancellationToken);
 
                 // Configure which server to which to connect.
-                saea.RemoteEndPoint = IPAddress.TryParse(host, out IPAddress address) ?
-                    (EndPoint)new IPEndPoint(address, port) :
-                    new DnsEndPoint(host, port);
+                saea.RemoteEndPoint = new DnsEndPoint(host, port);
 
                 // Initiate the connection.
                 if (Socket.ConnectAsync(SocketType.Stream, ProtocolType.Tcp, saea))