selftests/bpf: Fix test_lwt_seg6local.sh hangs

OpenBSD netcat (Debian patchlevel 1.195-2) does not seem to react to
SIGINT for whatever reason, causing prefix.pl to hang after
test_lwt_seg6local.sh exits due to netcat inheriting
test_lwt_seg6local.sh's file descriptors.

Fix by using SIGTERM instead.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200720101810.84299-1-iii@linux.ibm.com

tools/testing/selftests/bpf/test_lwt_seg6local.sh

@@ -140,7 +140,7 @@ ip netns exec ns6 sysctl net.ipv6.conf.veth10.seg6_enabled=1 > /dev/null
 ip netns exec ns6 nc -l -6 -u -d 7330 > $TMP_FILE &
 ip netns exec ns1 bash -c "echo 'foobar' | nc -w0 -6 -u -p 2121 -s fb00::1 fb00::6 7330"
 sleep 5 # wait enough time to ensure the UDP datagram arrived to the last segment
-kill -INT $!
+kill -TERM $!
 
 if [[ $(< $TMP_FILE) != "foobar" ]]; then
 	exit 1