Replace "-1" return with errno codes.

ENOMSG and EBADFD were choosen to do not cross with
standard recvmsg() errors (described in its man page).

This patch is need as preparation to making recv_msg()
be able to be non-block, and return EAGAIN and EWOULDBLOCK
in case of no data.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>