openib btl: add Soft iWARP device to the ini file

This enables IBM's software iWARP provider.  With this driver you can
run iWARP/RDMA over any ethernet NIC.  Useful for testing OMPI RDMA
logic without requiring an expensive RDMA adapter/infrastructure.

The Soft iWARP code is at: https://www.gitorious.org/softiwarp