opts: improved the TCP keepalive examples

docs/libcurl/opts/CURLOPT_TCP_KEEPALIVE.3

@@ -50,7 +50,7 @@ if(curl) {
   curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 120L);
 
   /* interval time between keep-alive probes: 60 seconds */
-  curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 60L);
+  curl_easy_setopt(curl, CURLOPT_TCP_KEEPINTVL, 60L);
 
   curl_easy_perform(curl);
 }

docs/libcurl/opts/CURLOPT_TCP_KEEPIDLE.3

@@ -48,7 +48,7 @@ if(curl) {
   curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 120L);
 
   /* interval time between keep-alive probes: 60 seconds */
-  curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 60L);
+  curl_easy_setopt(curl, CURLOPT_TCP_KEEPINTVL, 60L);
 
   curl_easy_perform(curl);
 }

docs/libcurl/opts/CURLOPT_TCP_KEEPINTVL.3

@@ -46,7 +46,7 @@ if(curl) {
   curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 120L);
 
   /* interval time between keep-alive probes: 60 seconds */
-  curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE, 60L);
+  curl_easy_setopt(curl, CURLOPT_TCP_KEEPINTVL, 60L);
 
   curl_easy_perform(curl);
 }