Fix uninitialised memory defect found by valgrind (#1582)

Fix "Conditional jump or move depends on
uninitialised value(s)" by initializing eiid after allocation.

Author: Arto Kinnunen

source/6LoWPAN/Thread/thread_common.c

@@ -717,6 +717,7 @@ void thread_child_id_request_info_init(thread_pending_child_id_req_t *child_info
 thread_pending_child_id_req_t *thread_child_id_request_allocate(void)
 {
     thread_pending_child_id_req_t *req = ns_dyn_mem_alloc(sizeof(thread_pending_child_id_req_t));
+    memset(req->eiid, 0 , 8);
     thread_child_id_request_info_init(req);
     return req;
 }