IB/iser: Add support for iser CM REQ additional info

Annex A12 of the IBTA spec defines additional information that needs
to be provided through the CM exchange relating to usage of ZBVA (Zero
Based VAs) and Send With Invalidate over an iSER connection.

Currently, the initiator sets both to not supported, but does provide
the header so that existing iSER targets can be patched to start
looking on the private data carried by the CM.

This is a preparation step to enable iSER with HW drivers for which
FMRs are not supported, such as mlx4 VF instances or new HW devices
which might support only FRWR (Fast Registration Work-Requests) along
the details of the IB_DEVICE_MEM_MGT_EXTENSIONS device capability.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>