ACK every N frames

[jwbensley]

Add a CLI option to ACK one in every N frames, otherwise ACK mode is very slow on a stable link with no drops.

[jwbensley]

Reported by @yskripachov

diff --git a/functions.c b/functions.c                                                                           
index a36ece5..faad4f4 100644                                                                                    
--- a/functions.c                                                                                                
+++ b/functions.c                                                                                                
@@ -2214,7 +2214,7 @@ void sync_settings(struct app_params *app_params,                                          
                 // TX has set ACK mode frame count                                                              
                 } else if (ntohs(*frame_headers->rx_sub_tlv_type) == TYPE_ACKCOUNT) {                           
                                                                                                                 
-                    test_params->f_ack_timeout = (uint32_t)ntohll(*frame_headers->rx_sub_tlv_value);            
+                    test_params->f_ack_count = (uint32_t)ntohll(*frame_headers->rx_sub_tlv_value);              
                     printf("ACK mode set to ACK every %" PRIu32 " frames\n", test_params->f_ack_count);         
                                                                                                                 
                 // TX has requested MTU sweep test