io_uring/kbuf: account ring io_buffer_list memory

Follow the non-ringed pbuf struct io_buffer_list allocations and account
it against the memcg. There is low chance of that being an actual
problem as ring provided buffer should either pin user memory or
allocate it, which is already accounted.

Cc: stable@vger.kernel.org # 6.1
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/3985218b50d341273cafff7234e1a7e6d0db9808.1747150490.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>