tests: Replace tcpdump with wlantest

This removes dependency on tcpdump by using an already included test
tool for capturing frames with Ethernet headers. There were some issues
in getting tcpdump working on Ubuntu 19.10, so this seems to be a clean
way of addressing that.

Signed-off-by: Jouni Malinen <j@w1.fi>

tests/hwsim/test_ap_open.py

@@ -17,6 +17,7 @@ import hwsim_utils
 from tshark import run_tshark
 from utils import *
 from wpasupplicant import WpaSupplicant
+from wlantest import WlantestCapture
 from test_ap_ht import set_world_reg
 
 @remote_compatible
@@ -911,10 +912,7 @@ def test_ap_open_layer_2_update(dev, apdev, params):
     cap = os.path.join(params['logdir'], prefix + "." + ifname + ".pcap")
 
     hapd = hostapd.add_ap(apdev[0], {"ssid": "open"})
-    capture = subprocess.Popen(['tcpdump', '-p', '-U', '-i', ifname,
-                                '-w', cap, '-s', '2000'],
-                               stdout=subprocess.PIPE,
-                               stderr=subprocess.PIPE)
+    wt = WlantestCapture(ifname, cap)
     time.sleep(1)
 
     dev[0].connect("open", key_mgmt="NONE", scan_freq="2412")
@@ -923,11 +921,7 @@ def test_ap_open_layer_2_update(dev, apdev, params):
     time.sleep(1)
     hwsim_utils.test_connectivity(dev[0], hapd)
     time.sleep(0.5)
-    capture.terminate()
-    res = capture.communicate()
-    logger.info("tcpdump stdout: " + res[0].decode())
-    logger.info("tcpdump stderr: " + res[1].decode())
-    time.sleep(0.5)
+    wt.close()
 
     # Check for Layer 2 Update frame and unexpected frames from the station
     # that did not fully complete authentication.