samples/bpf: run cleanup routines when receiving SIGTERM

Shahid Habib noticed that when xdp1 was killed from a different console the xdp
program was not cleaned-up properly in the kernel and it continued to forward
traffic.

Most of the applications in samples/bpf cleanup properly, but only when getting
SIGINT.  Since kill defaults to using SIGTERM, add support to cleanup when the
application receives either SIGINT or SIGTERM.

Signed-off-by: Andy Gospodarek <andy@greyhouse.net>
Reported-by: Shahid Habib <shahid.habib@broadcom.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/samples/bpf/sampleip_user.c b/samples/bpf/sampleip_user.c
index be59d7d..4ed690b 100644
--- a/samples/bpf/sampleip_user.c
+++ b/samples/bpf/sampleip_user.c
@@ -180,6 +180,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 	signal(SIGINT, int_exit);
+	signal(SIGTERM, int_exit);
 
 	/* do sampling */
 	printf("Sampling at %d Hertz for %d seconds. Ctrl-C also ends.\n",