Fix buffer read and write API naming

The letter 'x' in buffer_xread/buffer_xwrite attributes to xread/xwrite
functions being used inside

Signed-off-by: Marat Stanichenko <mstanichenko@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Add non-restarting buffer read and write API

Signed-off-by: Marat Stanichenko <mstanichenko@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
FIX: Use non-blocking reads for RX

xread function blocks the caller even if the underlying file descriptor
associated with the buffer is a non-blocking.  This patch makes FIX
receving engine be able to handle non-blocing file descriptors.

Signed-off-by: Marat Stanichenko <mstanichenko@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
FAST: Use non-blocking reads for RX

xread function blocks the caller even if the underlying
file descriptor associated with the buffer is a non-blocking.
This patch makes FAST receving engine be able to handle
non-blocing file descriptors.

Signed-off-by: Marat Stanichenko <mstanichenko@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>