randomise challenge tlv for parent request retries. (ARMmbed#1977)

Author: deepakvenugopal

source/DHCPv6_client/dhcpv6_client_service.c

@@ -206,7 +206,7 @@ int dhcp_client_get_global_address(int8_t interface, uint8_t dhcp_addr[static 16
 
     if (!prefix) {
         //NULL Definition will only check That Interface is not generated
-        if (libdhcpv6_nonTemporal_entry_get_by_instance(dhcp_client.libDhcp_instance) ) {
+        if (libdhcpv6_nonTemporal_entry_get_by_instance(dhcp_client.libDhcp_instance)) {
             //Already Created to same interface
             return -1;
         }

source/Service_Libs/mle_service/mle_service.c

@@ -228,6 +228,11 @@ static void mle_service_tr_timeout_handler(mle_service_msg_buf_t *cur_ptr)
         cur_ptr->tokens_delay = false;
     }
 
+    // Randomise Challenge TLV value
+    if (cur_ptr->challengePtr) {
+        randLIB_get_n_bytes_random(cur_ptr->challengePtr, cur_ptr->challengeLen);
+    }
+
     //Trig Buffer to socket
     mle_service_build_packet_send(srv_ptr, sec_params, cur_ptr);