bpf: Fix comment for helper bpf_current_task_under_cgroup()

This should be "current" not "skb".

Fixes: c6b5fb86 ("bpf: add documentation for eBPF helpers (42-50)")
Signed-off-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/bpf/20200910203314.70018-1-songliubraving@fb.com

include/uapi/linux/bpf.h

@@ -1447,8 +1447,8 @@ union bpf_attr {
  * 	Return
  * 		The return value depends on the result of the test, and can be:
  *
- * 		* 0, if the *skb* task belongs to the cgroup2.
- * 		* 1, if the *skb* task does not belong to the cgroup2.
+ *		* 0, if current task belongs to the cgroup2.
+ *		* 1, if current task does not belong to the cgroup2.
  * 		* A negative error code, if an error occurred.
  *
  * long bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)

tools/include/uapi/linux/bpf.h

@@ -1447,8 +1447,8 @@ union bpf_attr {
  * 	Return
  * 		The return value depends on the result of the test, and can be:
  *
- * 		* 0, if the *skb* task belongs to the cgroup2.
- * 		* 1, if the *skb* task does not belong to the cgroup2.
+ *		* 0, if current task belongs to the cgroup2.
+ *		* 1, if current task does not belong to the cgroup2.
  * 		* A negative error code, if an error occurred.
  *
  * long bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)