docs: bpf: Document BPF_RB_OVERWRITE_POS in bpf_ringbuf_query

BPF_RB_OVERWRITE_POS is supported by bpf_ringbuf_query() but was missing
from the helper documentation. Add it to the flags list in both the
kernel UAPI header and its tools/ mirror.

Signed-off-by: Jianlin Shi <shijianlin11@foxmail.com>
Acked-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/bpf/tencent_22134645443B75ED907D2A85A47AD554A709@qq.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

include/uapi/linux/bpf.h

@@ -4735,6 +4735,7 @@ union bpf_attr {
  *		* **BPF_RB_RING_SIZE**: The size of ring buffer.
  *		* **BPF_RB_CONS_POS**: Consumer position (can wrap around).
  *		* **BPF_RB_PROD_POS**: Producer(s) position (can wrap around).
+ *		* **BPF_RB_OVERWRITE_POS**: Overwrite position (can wrap around).
  *
  *		Data returned is just a momentary snapshot of actual values
  *		and could be inaccurate, so this facility should be used to