bpf: sockmap, on update propagate errors back to userspace

When an error happens in the update sockmap element logic also pass
the err up to the user.

Fixes: e5cd3abcb3 ("bpf: sockmap, refactor sockmap routines to work with hashmap")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/sockmap.c

@@ -1875,7 +1875,7 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops,
 		write_unlock_bh(&osock->sk_callback_lock);
 	}
 out:
-	return 0;
+	return err;
 }
 
 int sock_map_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type)