FAST: send/recv functionality for non-socket descriptors

recv() and sendmsg() are intended for sockets only.  fast_orderbook and
fast_parser support various data streams. Library FAST engine should
support them also.

Reported-by: Pavel Kostikov
Signed-off-by: Marat Stanichenko <mstanichenko@gmail.com>
Signed-off-by: Pekka Enberg <penberg@iki.fi>