Corrected GKH initiation on supplicant

Creates now always instance for GTK if previous instance is terminating.
This enables handling repeated GTK sets for different keys (up to three
keys migth be set). This also works for repeated messages (same message
counter). They are routed to created instance and ignored. Instance
clears when it timeouts. If valid message is received, it is handled
by instance and replied normally.

source/6LoWPAN/ws/ws_pae_supp.c

@@ -1011,7 +1011,13 @@ static kmp_api_t *ws_pae_supp_kmp_incoming_ind(kmp_service_t *service, kmp_type_
 
     // Check if ongoing
     kmp_api_t *kmp = ws_pae_lib_kmp_list_type_get(&pae_supp->entry.kmp_list, type);
-    if (kmp) {
+    /* If kmp receiving is enabled or it is not GKH, routes message to existing KMP.
+
+       For GKH creates an instance to handle message. If message is not valid (e.g. repeated
+       message counter), GKH ignores message and waits for timeout. All further messages
+       are routed to that instance. If valid message arrives, GKH instance handles the
+       message, replies to authenticator and terminates. */
+    if (kmp && (!kmp_api_receive_disable(kmp) || type != IEEE_802_11_GKH)) {
         return kmp;
     }