block/iscsi: Adding new iSER transport layer option

block/iscsi: Adding new iSER transport layer option

iSER is a new transport layer supported in Libiscsi,
iSER provides a zero-copy RDMA capable interface that can
improve performance.

In order to use the new iSER transport one need to have RDMA supported HW
and to choose iser as the protocol name in Libiscsi URI.

For now iSER memory buffers are pre-allocated and pre-registered,
hence in order to work with iSER from QEMU, one need to enable
MEMLOCK attribute in the VM to be large enough for all iSER buffers and RDMA
resources.

Signed-off-by: Roy Shterman <roysh@mellanox.com>
Message-Id: <1476000896-18632-3-git-send-email-roysh@mellanox.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>