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>

samples/bpf/offwaketime_user.c

@@ -100,6 +100,7 @@ int main(int argc, char **argv)
 	setrlimit(RLIMIT_MEMLOCK, &r);
 
 	signal(SIGINT, int_exit);
+	signal(SIGTERM, int_exit);
 
 	if (load_kallsyms()) {
 		printf("failed to process /proc/kallsyms\n");