Move buf_ring_* functions into BufferRing type as methods

add IoUring tee syscall functionality

adapt ReadBuffer union idea for read_fixed to support fixed read and readv

Use same idea and create a WriteBuffer type for write() and write_fixed()

ignored flags for splice and tee lets see if they become important in
the future

add a get_data helper to Cqe

Signed-off-by: Bernard Assan <[email protected]>

Author: bernardassan