bpf: Fix iter/task tid filtering

In userspace, you can add a tid filter by setting
the "task.tid" field for "bpf_iter_link_info".
However, `get_pid_task` when called for the
`BPF_TASK_ITER_TID` type should have been using
`PIDTYPE_PID` (tid) instead of `PIDTYPE_TGID` (pid).

Fixes: f0d74c4d ("bpf: Parameterize task iterators.")
Signed-off-by: Jordan Rome <linux@jordanrome.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241016210048.1213935-1-linux@jordanrome.com

kernel/bpf/task_iter.c

@@ -99,7 +99,7 @@ static struct task_struct *task_seq_get_next(struct bpf_iter_seq_task_common *co
 		rcu_read_lock();
 		pid = find_pid_ns(common->pid, common->ns);
 		if (pid) {
-			task = get_pid_task(pid, PIDTYPE_TGID);
+			task = get_pid_task(pid, PIDTYPE_PID);
 			*tid = common->pid;
 		}
 		rcu_read_unlock();