man: Add `io_uring_enter2()` function signature
man: Add `io_uring_enter2()` function signature

Since kernel 5.11, liburing has io_uring_enter2() wrapper which behaves
just like the io_uring_enter(), but with an extra argument for
`IORING_ENTER_EXT_ARG` case. Add this function signature to the
synopsis part. Also, change the function name in "kernel 5.11" part to
io_uring_enter2().

Suggested-by: Caleb Sander <fa2ca9518879ab9dbdedcf10ba3b1999589f7d8b@purestorage.com>
Signed-off-by: Ammar Faizi <a8266392a329a5c7b5ab982a8996391d75b6438e@gnuweeb.org>
Link: 245f28ff3bf50e1bdb3aa39053cefd1c07d9e5cd@intel.com
Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing