When reading from nbd device, we need to receive all the data after
receiving reply packet from the server - otherwise such request will never
be ended.

If socket is closed right after accepting reply control packet and in the
middle of waiting for read data, nbd_read_stat() returns NULL and
nbd_end_request() is not called.

This patch fixes it.
Signed-off-by: Michal Feix <michal@feix.cz>
Acked-by: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>