runtests.pl: fix startup of IPv6 servers

Commit curl-7_23_1-143-g8218064 changed the parameter of
responsive_http_server to accept types other than IPv6 (converting
from a boolean to a string), but only considered the lower-case "ipv6"
and not the "IPv6" variant. This caused all servers to start in IPv4
mode instead.

This patch converts the remaining cases to "ipv6". While not strictly
necessary for the run*server variants, these got also converted for
consistency and to prevent future errors.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>

tests/runtests.pl

@@ -4203,7 +4203,7 @@ sub startservers {
         }
         elsif($what eq "http-ipv6") {
             if($torture && $run{'http-ipv6'} &&
-               !responsive_http_server("http", $verbose, "IPv6", $HTTP6PORT)) {
+               !responsive_http_server("http", $verbose, "ipv6", $HTTP6PORT)) {
                 stopserver('http-ipv6');
             }
             if(!$run{'http-ipv6'}) {
@@ -4250,11 +4250,11 @@ sub startservers {
         }
         elsif($what eq "rtsp-ipv6") {
             if($torture && $run{'rtsp-ipv6'} &&
-               !responsive_rtsp_server($verbose, "IPv6")) {
+               !responsive_rtsp_server($verbose, "ipv6")) {
                 stopserver('rtsp-ipv6');
             }
             if(!$run{'rtsp-ipv6'}) {
-                ($pid, $pid2) = runrtspserver($verbose, "IPv6");
+                ($pid, $pid2) = runrtspserver($verbose, "ipv6");
                 if($pid <= 0) {
                     return "failed starting RTSP-IPv6 server";
                 }
@@ -4362,11 +4362,11 @@ sub startservers {
                 return "no gnutls-serv";
             }
             if($torture && $run{'httptls-ipv6'} &&
-               !responsive_httptls_server($verbose, "IPv6")) {
+               !responsive_httptls_server($verbose, "ipv6")) {
                 stopserver('httptls-ipv6');
             }
             if(!$run{'httptls-ipv6'}) {
-                ($pid, $pid2) = runhttptlsserver($verbose, "IPv6");
+                ($pid, $pid2) = runhttptlsserver($verbose, "ipv6");
                 if($pid <= 0) {
                     return "failed starting HTTPTLS-IPv6 server (gnutls-serv)";
                 }
@@ -4391,11 +4391,11 @@ sub startservers {
         }
         elsif($what eq "tftp-ipv6") {
             if($torture && $run{'tftp-ipv6'} &&
-               !responsive_tftp_server("", $verbose, "IPv6")) {
+               !responsive_tftp_server("", $verbose, "ipv6")) {
                 stopserver('tftp-ipv6');
             }
             if(!$run{'tftp-ipv6'}) {
-                ($pid, $pid2) = runtftpserver("", $verbose, "IPv6");
+                ($pid, $pid2) = runtftpserver("", $verbose, "ipv6");
                 if($pid <= 0) {
                     return "failed starting TFTP-IPv6 server";
                 }