common/multipath-over-rdma, tests/srp: Make it easy to use siw instead of rdma_rxe

common/multipath-over-rdma, tests/srp: Make it easy to use siw instead of rdma_rxe

Make all_primary_gids() return GIDs with zero suffix since SoftiWARP
GIDs have such a suffix. Add SoftiWARP support in start_soft_rdma() and
stop_soft_rdma(). Make do_rdma_cm_login() submit the source IP address
and scope ID to the SRP initiator driver since that information is
essential to establish an IPv6 connection between link-local addresses.
Iterate over RDMA ports instead of UMAD device nodes in log_in() since
no UMAD device node is associated with SoftiWARP ports. In start_lio_srpt(),
use the GID format to identify SoftiWARP ports since the GID suffix for
these ports is zero.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>