Also read stream limits after authentication

The [business rules](https://xmpp.org/extensions/xep-0478.html#rules)
mention the following:

> It is acceptable for the limits on a stream to change whenever new stream features are announced - such as before and after authentication of the connecting entity.

The first detection of the stream limits is not deleted as there is also
ANONYMOUS authentication.

xmpp.go

@@ -765,6 +765,20 @@ func (c *Client) init(o *Options) error {
 	if f, err = c.startStream(o, domain); err != nil {
 		return err
 	}
+	// Make the max. stanza size limit available.
+	if f.Limits.MaxBytes != "" {
+		c.LimitMaxBytes, err = strconv.Atoi(f.Limits.MaxBytes)
+		if err != nil {
+			c.LimitMaxBytes = 0
+		}
+	}
+	// Make the servers time limit after which it might consider the stream idle available.
+	if f.Limits.IdleSeconds != "" {
+		c.LimitIdleSeconds, err = strconv.Atoi(f.Limits.IdleSeconds)
+		if err != nil {
+			c.LimitIdleSeconds = 0
+		}
+	}
 
 	// Generate a unique cookie
 	cookie := getCookie()