system-traffic: Properly stop dangling ping after geneve test.
Ping process remains in the system after the test.  Using a proper
macro that will correctly register it for stopping at cleanup stage.
Fixes: ("system-traffic: Check frozen state handling with TLV map change")
@@ -758,7 +758,7 @@ NS_CHECK_EXEC([at_ns0], [ping -q -c 3 10.1.1.100 | FORMAT_PING], [0], [dnl
])
dnl Test OVS handles TLV map modifictions properly when restores frozen state.
-NS_CHECK_EXEC([at_ns0], [ping 10.1.1.100 > /dev/null &])
+NETNS_DAEMONIZE([at_ns0], [ping 10.1.1.100 > /dev/null], [ping0.pid])
AT_CHECK([ovs-ofctl add-tlv-map br0 "{class=0xffff,type=0x88,len=4}->tun_metadata1"])
sleep 1
