ibmvscsi: Fix host config length field overflow

ibmvscsi: Fix host config length field overflow

commit 225c56960fcafeccc2b6304f96cd3f0dbf42a16a upstream.

The length field in the host config packet is only 16-bit long, so
passing it 0x10000 (64K which is our standard PAGE_SIZE) doesn't
work and result in an empty config from the server.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Robert Jennings <rcj@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>