graid: Set G_CF_DIRECT_SEND for task consumer.

Unlike normal consumers all taste consumer I/O is synchronous, done
with g_read_data() and without any locks held. It makes no sense to
delegate I/O submission to g_down thread.

This should remove number of context switches during disk retaste.

MFC after: 2 weeks

(cherry picked from commit 0d8cec7658d50e4190899376330c2c1eb5d8c659)