tests: decrease risk of flaky failures of ovn -- CoPP system test

The test was often failing with a meter of 10 pps while generating 100 packets.
When the 100 packets generation takes more than 100 msec, the test fails.
This happens from time to time in upstream ci.
Reducing the number of generated packets to 40 should reduce number of flakes.

Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Acked-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Mark Michelson <mmichels@redhat.com>

tests/system-ovn.at

@@ -7190,7 +7190,7 @@ NS_EXEC([sw01], [tcpdump -l -n -i sw01 icmp -Q in > reject.pcap &])
 check ovn-nbctl --may-exist meter-add acl-meter drop 10 pktps 0
 ip netns exec sw01 scapy -H <<-EOF
 p = IP(src="192.168.1.2", dst="192.168.1.1") / UDP(dport = 12345) / Raw(b"X"*64)
-send (p, iface='sw01', loop = 0, verbose = 0, count = 100)
+send (p, iface='sw01', loop = 0, verbose = 0, count = 40)
 EOF
 
 # 10pps