tests: Fix time dependency in overlapping flows modification test.

On slow systems or at high testsuite concurrency sending 256 packets
can take more than 10 seconds.  This is causing expiration of one of
the flows and a subsequent test failure.

Use time warping instead to avoid the time dependency.

Fixes: 21410ff ("dpif-netdev: Fix dpif_netdev_flow_put.")
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2023-August/052623.html
Reported-by: Sangeetha Elumalai <sangeethaeng2017@gmail.com>
Reviewed-by: Frode Nordahl <frode.nordahl@canonical.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

tests/pmd.at

@@ -1355,18 +1355,22 @@ AT_CHECK([echo 'table=0,in_port=p1,ip,nw_dst=10.1.0.0/16 actions=ct(commit)' | d
           ovs-ofctl --bundle replace-flows br0 -])
 AT_CHECK([ovs-appctl revalidator/wait])
 
+dnl Prevent flows from expiring.
+AT_CHECK([ovs-appctl time/stop])
+
 AT_CHECK([ovs-appctl netdev-dummy/receive p1 'ipv4(src=10.0.0.1,dst=10.1.0.2,proto=6),tcp(src=1,dst=2)'])
 OVS_WAIT_UNTIL_EQUAL([ovs-appctl dpctl/dump-flows | sed 's/.*core: [[0-9]]*//' | strip_xout_keep_actions], [
 recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(dst=10.1.0.2/255.255.0.0,frag=no), packets:0, bytes:0, used:never, actions:ct(commit)
 recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(dst=10.1.2.2/255.255.255.0,frag=no), packets:0, bytes:0, used:0.0s, actions:ct(commit)])
 
-dnl Hold the prefix 10.1.2.2/24 by another 10s.
-AT_CHECK([ovs-appctl netdev-dummy/receive p1 'ipv4(src=10.0.0.1,dst=10.1.2.2,proto=6),tcp(src=1,dst=2)'])
 dnl Send more 10.1.0.2 to make 10.1.0.0/16 tuple prepend 10.1.2.0/24 tuple in the pvector of subtables.
 for i in $(seq 0 256); do
   AT_CHECK([ovs-appctl netdev-dummy/receive p1 'ipv4(src=10.0.0.1,dst=10.1.0.2,proto=6),tcp(src=1,dst=2)'])
 done
 
+dnl Warp time enough to trigger subtable optimization.
+AT_CHECK([ovs-appctl time/warp 500 2000], [0], [ignore])
+
 AT_CHECK([echo 'table=0,in_port=p1,ip,nw_dst=10.1.0.0/16 actions=p2' | dnl
           ovs-ofctl --bundle replace-flows br0 -])