selftests/bpf: More compatible nc options in test_tc_edt

Out of the three nc implementations widely in use, at least two (BSD netcat
and nmap-ncat) do not support -l combined with -s. Modify the nc invocation
to be accepted by all of them.

Fixes: 7df5e3db ("selftests: bpf: tc-bpf flow shaping with EDT")
Signed-off-by: NJiri Benc <jbenc@redhat.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NPeter Oskolkov <posk@google.com>
Link: https://lore.kernel.org/bpf/f5bf07dccd8b552a76c84d49e80b86c5aa071122.1571400024.git.jbenc@redhat.com

tools/testing/selftests/bpf/test_tc_edt.sh

@@ -59,7 +59,7 @@ ip netns exec ${NS_SRC} tc filter add dev veth_src egress \
 
 # start the listener
 ip netns exec ${NS_DST} bash -c \
-	"nc -4 -l -s ${IP_DST} -p 9000 >/dev/null &"
+	"nc -4 -l -p 9000 >/dev/null &"
 declare -i NC_PID=$!
 sleep 1