flaky system test: conntrack - SNAT with port range with exhaustion

[Frode Nordahl]

The system test named "conntrack - SNAT with port range with exhaustion" fails intermittently.

Excerpt of logs from one failed test run:
wget 10.1.1.2 -t 1 -T 1 --retry-connrefused -v -o wget0.log
NS_EXEC_HEREDOC
10.1.1.240 - - [22/Oct/2023 11:44:06] "GET / HTTP/1.1" 200 -
../../tests/system-traffic.at:5876: ip netns exec at_ns0 sh << NS_EXEC_HEREDOC
wget 10.1.1.2 -t 1 -T 1 --retry-connrefused -v -o wget0.log
NS_EXEC_HEREDOC
../../tests/system-traffic.at:5878: ovs-appctl dpctl/dump-conntrack | grep "dst=10.1.1.2" | sed -e 's/port=[0-9]*/port=<cleared>/g' -e 's/id=[0-9]*/id=<cleared>/g' -e 's/state=[0-9_A-Z]*/state=<cleared>/g' | sort | uniq | sed -e 's/dst=10.1.1.2[45][0-9]/dst=10.1.1.2XX/' | uniq
--- - 2023-10-22 11:44:07.581599299 +0200
+++ /tmp/autopkgtest.nHwTfd/build.rHl/src/_debian/tests/system-kmod-testsuite.dir/at-groups/126/stdout 2023-10-22 11:44:07.574615972 +0200
@@ -1,2 +1,4 @@
+icmp,orig=(src=10.1.1.1,dst=10.1.1.2,id=<cleared>,type=8,code=0),reply=(src=10.1.1.2,dst=10.1.1.1,id=<cleared>,type=0,code=0)
+igmp,orig=(src=10.1.1.2,dst=224.0.0.22,sport=<cleared>,dport=<cleared>),reply=(src=224.0.0.22,dst=10.1.1.2,sport=<cleared>,dport=<cleared>)
 tcp,orig=(src=10.1.1.1,dst=10.1.1.2,sport=<cleared>,dport=<cleared>),reply=(src=10.1.1.2,dst=10.1.1.2XX,sport=<cleared>,dport=<cleared>),zone=1,protoinfo=(state=<cleared>)