test: netns: Let the default ping timeout be tuned in the topology

QEMU systems seem work fine with the 5s timeout, whereas some physical
devices can't quite keep up with that.

Let the slower systems indicate that they need a bit more time without
punishing faster ones with a longer default.

test/infamy/netns.py

@@ -5,6 +5,8 @@ import random
 import subprocess
 import time
 
+from . import env
+
 __libc = ctypes.CDLL(None)
 CLONE_NEWUSER = 0x10000000
 CLONE_NEWNET  = 0x40000000
@@ -19,6 +21,7 @@ class IsolatedMacVlan:
     def __init__(self, parent, ifname="iface", lo=True):
         self.sleeper = None
         self.parent, self.ifname, self.lo = parent, ifname, lo
+        self.ping_timeout = env.ENV.attr("ping_timeout", 5)
 
     def __enter__(self):
         self.sleeper = subprocess.Popen(["unshare", "-r", "-n", "sh", "-c",
@@ -162,7 +165,9 @@ class IsolatedMacVlan:
             result.append(l)
         return result
 
-    def ping(self, daddr, timeout=5):
+    def ping(self, daddr, timeout=None):
+        timeout = timeout if timeout else self.ping_timeout
+
         return self.run(["timeout", str(timeout), "/bin/sh"], text=True, check=True,
                         stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
                         input=f"while :; do ping -c1 -w1 {daddr} && break; done")