rds: reduce memory footprint for RDS when transport is RDMA

rds: reduce memory footprint for RDS when transport is RDMA

RDS over IB does not use multipath RDS, so the array
of additional rds_conn_path structures is always superfluous
in this case. Reduce the memory footprint of the rds module
by making this a dynamic allocation predicated on whether
the transport is mp_capable.

Orabug: 26412003

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Tested-by: Efrain Galaviz <efrain.galaviz@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Avinash Repaka <avinash.repaka@oracle.com>
(cherry picked from commit 840df162b3eb3ec02e2613411fad1285a0017c13)