samples/bpf: Use getppid instead of getpgrp for array map stress

When cross-compiling the bpf sample map_perf_test for aarch64, I find that
__NR_getpgrp is undefined. This causes build errors. This syscall is deprecated
and requires defining __ARCH_WANT_SYSCALL_DEPRECATED. To avoid having to define
that, just use a different syscall (getppid) for the array map stress test.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

samples/bpf/map_perf_test_kern.c

@@ -266,7 +266,7 @@ int stress_hash_map_lookup(struct pt_regs *ctx)
 	return 0;
 }
 
-SEC("kprobe/sys_getpgrp")
+SEC("kprobe/sys_getppid")
 int stress_array_map_lookup(struct pt_regs *ctx)
 {
 	u32 key = 1, i;