tests: Fix load balancing system-tests.

As in [0], multiple load balancing system tests are randomly failing from
time to time as they check that, after 10 requests sent to a load
balancer, all backends are at least reached once. Statistically, this is
failing from time to time.
[1] fixed such issues, but there is a new occurrence.

[0] https://github.com/ovsrobot/ovn/actions/runs/27547031217/job/81423590350
[1] c906da4: tests: Fixed load balancing system-tests

Fixes: da55294 ("northd: Do not drop ip traffic with destination vip expressed via template vars.")
Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Signed-off-by: Mark Michelson <mmichels@redhat.com>

Author: simonartxavier

tests/system-ovn.at

@@ -17733,7 +17733,7 @@ NETNS_START_TCPDUMP([foo1], [-neei foo1 src 20.0.0.2 and tcp], [foo1])
 NETNS_START_TCPDUMP([bar1], [-neei bar1 src 20.0.0.2 and tcp], [bar1])
 
 check ovs-appctl dpctl/flush-conntrack
-for i in $(seq 10); do
+for i in $(seq 20); do
     NS_CHECK_EXEC([alice1], [wget 172.16.1.1:8000 -t 5 -T 1 --retry-connrefused -v -o wget$i.log])
 done