fix: fix burst mode throttle checking (#898)

When burst mode is configured for unlimited rate (-b0) but with a
specific packet burst value (e.g. /1000), iperf only sends packets once,
after that the iperf_check_throttle function gets called and sets
green_light=0 due to the rate value being 0 and average calculated rate
always being higher than 0.

The iperf_check_throttle function is designed to be skipped in case the
target rate is unlimited or if a specific burst value was configured,
however this skip is only utilized in one place where the function is
called leading to the situation above.

This can be fixed by moving the "skip throttling" condition directly
inside the iperf_check_throttle function.

Signed-off-by: Ondrej Lichtner <olichtne@redhat.com>

src/iperf_api.c

@@ -1411,7 +1411,7 @@ iperf_check_throttle(struct iperf_stream *sp, struct iperf_time *nowP)
     double seconds;
     uint64_t bits_per_second;
 
-    if (sp->test->done)
+    if (sp->test->done || sp->test->settings->rate == 0 || sp->test->settings->burst != 0)
         return;
     iperf_time_diff(&sp->result->start_time_fixed, nowP, &temp_time);
     seconds = iperf_time_in_secs(&temp_time);
@@ -1456,8 +1456,7 @@ iperf_send(struct iperf_test *test, fd_set *write_setP)
 		streams_active = 1;
 		test->bytes_sent += r;
 		++test->blocks_sent;
-		if (test->settings->rate != 0 && test->settings->burst == 0)
-		    iperf_check_throttle(sp, &now);
+		iperf_check_throttle(sp, &now);
 		if (multisend > 1 && test->settings->bytes != 0 && test->bytes_sent >= test->settings->bytes)
 		    break;
 		if (multisend > 1 && test->settings->blocks != 0 && test->blocks_sent >= test->settings->blocks)