testing: Fix route-based/net2net-xfrmi-ike scenario

On newer systems, the upper hard limit for open file descriptors (see
`ulimit -H -n`) was increased from 4096 to 524288.  Due to how python-daemon
closes potentially open file descriptors (basically stores them in a set,
removes those excluded by config, and loops through all of them), the updown
script was either killed immediately (by the OOM killer) or not ready yet
when updown events occurred.

testing/tests/route-based/net2net-xfrmi-ike/hosts/sun/etc/updown.py

@@ -6,6 +6,7 @@ import daemon
 import logging
 from logging.handlers import SysLogHandler
 import subprocess
+import resource
 
 
 logger = logging.getLogger('updownLogger')
@@ -54,6 +55,13 @@ def install_routes(ike_sa):
         subprocess.call(["ip", "route", "add", ts, "dev", ifname_out])
 
 
+# the hard limit (second number) is the value used by python-daemon when closing
+# potentially open file descriptors while daemonizing.  since the default is
+# 524288 on newer systems, this can take quite a while, and due to how this
+# range of FDs is handled internally (as set) it can even trigger the OOM killer
+resource.setrlimit(resource.RLIMIT_NOFILE, (256, 256))
+
+
 # daemonize and run parallel to the IKE daemon
 with daemon.DaemonContext():
     logger.debug("starting Python updown listener")