For the platforms that don't support MSG_DONTWAIT the reader
socket in mailbox_t was kept in non-blocking state and flipped
to blocking state and back when blocking read was requested.
Now, the state is preserved between calls and flipped only
if different type of operation (block vs. non-block) is
requested.
Signed-off-by: Fabien Ninoles <fabien@tzone.org>
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>