IB/hfi1: Add the transmit side of a datagram ipoib RDMA netdev

IB/hfi1: Add the transmit side of a datagram ipoib RDMA netdev

This implements the transmit side of the multiple transmit queue RDMA
netdev used to accelerate ipoib.  The receive side remains the ipoib
internal implementation.

The init/unint/open/stop netdev operations are saved off and called by the
versions within the hfi1 netdev in order to initialize the connected mode
resources present in ipoib thus allowing us to switch modes between
datagram and connected.

The datagram queue pair instantiated by the ipoib ulp is used by this
implementation for its queue pair number and to register with multicast.

The above queue pair is not used on transmit other than its qpn as the
verbs layer is skipped and packets are directly submitted to the sdma
engines.

Link: https://lore.kernel.org/r/20200511160554.173205.1369.stgit@awfm-01.aw.intel.com
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Gary Leshner <Gary.S.Leshner@intel.com>
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>