updating list of supported sysctls

Author: kalexand-rh

admin_guide/sysctls.adoc

@@ -89,11 +89,12 @@ a pod.
 
 By far, most of the namespaced sysctls are not necessarily considered safe.
 
-For {product-title} 3.3.1, the following sysctls are supported (whitelisted) in
-the safe set:
+Currently, {product-title} supports, or whitelists, the following sysctls
+in the safe set:
 
 - *_kernel.shm_rmid_forced_*
 - *_net.ipv4.ip_local_port_range_*
+- *_net.ipv4.tcp_syncookies_*
 
 This list will be extended in future versions when the kubelet supports better
 isolation mechanisms.