nvme-rdma: Fix transfer length when write_generate/read_verify are 0

When the block layer doesn't generate/verify metadata, the SG length is
smaller than the transfer length. This is because the SG length doesn't
include the metadata length that is added by the HW on the wire. The
target failes those commands with "Data SGL Length Invalid" by comparing
the transfer length and the SG length. Fix it by adding the metadata
length to the transfer length when there is no metadata SGL. The bug
reproduces when setting read_verify/write_generate configs to 0 at the
child multipath device or at the primary device when NVMe multipath is
disabled.

Note that setting those configs to 0 on the multipath device (ns_head)
doesn't have any impact on the I/Os.

Fixes: 5ec5d3bd ("nvme-rdma: add metadata/T10-PI support")
Signed-off-by: Israel Rukshin <israelr@nvidia.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>