selftests/bpf: More compatible nc options in test_lwt_ip_encap

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: 17a90a78 ("selftests/bpf: test that GSO works in lwt_ip_encap")
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/9f177682c387f3f943bb64d849e6c6774df3c5b4.1570539863.git.jbenc@redhat.com

tools/testing/selftests/bpf/test_lwt_ip_encap.sh

@@ -314,15 +314,15 @@ test_gso()
 	command -v nc >/dev/null 2>&1 || \
 		{ echo >&2 "nc is not available: skipping TSO tests"; return; }
 
-	# listen on IPv*_DST, capture TCP into $TMPFILE
+	# listen on port 9000, capture TCP into $TMPFILE
 	if [ "${PROTO}" == "IPv4" ] ; then
 		IP_DST=${IPv4_DST}
 		ip netns exec ${NS3} bash -c \
-			"nc -4 -l -s ${IPv4_DST} -p 9000 > ${TMPFILE} &"
+			"nc -4 -l -p 9000 > ${TMPFILE} &"
 	elif [ "${PROTO}" == "IPv6" ] ; then
 		IP_DST=${IPv6_DST}
 		ip netns exec ${NS3} bash -c \
-			"nc -6 -l -s ${IPv6_DST} -p 9000 > ${TMPFILE} &"
+			"nc -6 -l -p 9000 > ${TMPFILE} &"
 		RET=$?
 	else
 		echo "    test_gso: unknown PROTO: ${PROTO}"