tests: fixed system test "LR with SNAT fragmentation needed for exter…

…nal server".

The test was sometimes failing if IPv6 packets were received.

Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
(cherry picked from commit 17f20bc)

tests/system-ovn-kmod.at

@@ -321,12 +321,12 @@ NETNS_DAEMONIZE([server], [$PYTHON3 ./server.py > server.log], [server.pid])
 
 dnl Collect packets on server side.
 NETNS_DAEMONIZE([server], [tcpdump -l -U -i server -vnne \
-          'icmp or udp' > server.tcpdump 2>server_err], [tcpdump0.pid])
+          'ip and (icmp or udp)' > server.tcpdump 2>server_err], [tcpdump0.pid])
 OVS_WAIT_UNTIL([grep "listening" server_err])
 
 dnl Collect packets on client side.
 NETNS_DAEMONIZE([client], [tcpdump -l -U -i client -vnne \
-          'icmp or udp' > client.tcpdump 2>client_err], [tcpdump1.pid])
+          'ip and (icmp or udp)' > client.tcpdump 2>client_err], [tcpdump1.pid])
 OVS_WAIT_UNTIL([grep "listening" client_err])
 
 dnl Send two packets to the server with a short interval.