MFC:

MFC:
Improve apply callback error reporting:
Before this patch callback returned result of the last finished call chain.
Now it returns last nonzero result from all call chain results in this request.

As soon as this improvement gives reliable error reporting, it is now possible
to remove dirty workaround in ng_socket, made to return ENOBUFS error statuses
of request-response operations. That workaround was responsible for returning
ENOBUFS errors to completely unrelated requests working at the same time
on socket.