Tests: unbreak ssl_stapling.t after IO::Socket::SSL refactoring.

Previously, the test used to check the established SSL/TLS protocol version
using Net::SSLeay on the client side.  Now it is provided on the server side
within a server response.  Added missing bits to make this actually work.

Author: pluknet

ssl_stapling.t

@@ -57,6 +57,8 @@ http {
 
     ssl_ciphers DEFAULT:ECCdraft;
 
+    add_header X-SSL-Protocol $ssl_protocol always;
+
     server {
         listen       127.0.0.1:8443 ssl;
         listen       127.0.0.1:8080;
@@ -341,7 +343,7 @@ sub staple {
 }
 
 sub test_tls13 {
-	return http_get('/', start => 1, SSL => 1) =~ /TLSv1.3/;
+	return http_get('/', SSL => 1) =~ /TLSv1.3/;
 }
 
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