selftests: drv-net: Make rand_port() get a port more reliably

JIRA: https://issues.redhat.com/browse/RHEL-75603

commit 0163250
Author: Gal Pressman <gal@nvidia.com>
Date:   Mon Feb 24 19:44:15 2025 +0200

    selftests: drv-net: Make rand_port() get a port more reliably

    Instead of guessing a port and checking whether it's available, get an
    available port from the OS.

    Reviewed-by: Nimrod Oren <noren@nvidia.com>
    Signed-off-by: Gal Pressman <gal@nvidia.com>
    Link: https://patch.msgid.link/20250224174416.499070-4-gal@nvidia.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Mohammad Heib <mheib@redhat.com>

Author: mohammadheib

tools/testing/selftests/net/lib/py/utils.py

@@ -125,18 +125,11 @@ def ethtool(args, json=None, ns=None, host=None):
 
 def rand_port():
     """
-    Get a random unprivileged port, try to make sure it's not already used.
+    Get a random unprivileged port.
     """
-    for _ in range(1000):
-        port = random.randint(10000, 65535)
-        try:
-            with socket.socket(socket.AF_INET6, socket.SOCK_STREAM) as s:
-                s.bind(("", port))
-            return port
-        except OSError as e:
-            if e.errno != errno.EADDRINUSE:
-                raise
-    raise Exception("Can't find any free unprivileged port")
+    with socket.socket(socket.AF_INET6, socket.SOCK_STREAM) as s:
+        s.bind(("", 0))
+        return s.getsockname()[1]
 
 
 def wait_port_listen(port, proto="tcp", ns=None, host=None, sleep=0.005, deadline=5):