iperf3: increase extra timeout to 30s

10s was too short and has still caused tests to fail because they were
stopped just before the iperf finished.

30s seems to be enought and has passed multiple times so far

Change-Id: I80b732a060356aa98882ff0e8b5debaf623ba0fb
diff --git a/src/osmo_gsm_tester/obj/iperf3.py b/src/osmo_gsm_tester/obj/iperf3.py
index ee62159..13fd455 100644
--- a/src/osmo_gsm_tester/obj/iperf3.py
+++ b/src/osmo_gsm_tester/obj/iperf3.py
@@ -250,7 +250,7 @@
             proc = self.prepare_test_proc_locally(dir, netns, time_sec, proto == IPerf3Client.PROTO_UDP, bitrate)
         else:
             proc = self.prepare_test_proc_remotely(dir, netns, time_sec, proto == IPerf3Client.PROTO_UDP, bitrate)
-        proc.set_default_wait_timeout(time_sec + 10) # leave 10 extra sec for remote run, ctrl conn establishment, etc.
+        proc.set_default_wait_timeout(time_sec + 30) # leave 30 extra sec for remote run, ctrl conn establishment, etc.
         return proc
 
     def prepare_test_proc_remotely(self, dir, netns, time_sec, use_udp, bitrate):