IB/ipoib: Improve latency in ipoib/cm connection formation

IB/ipoib: Improve latency in ipoib/cm connection formation

Currently IPoIB connected mode queries the device to get the pkey table
entry during connection formation. This will increase the time taken to
form the connection, especially when limited pkeys are in use.  This gets
worse when multiple connection attempts are done in parallel.

Since ipoib interfaces are locked to a single pkey, use the pkey index
that was determined at link up time instead of searching for anything.

This improved the latency from 500ms to 1ms on an internal setup.

Link: https://lore.kernel.org/r/1618338965-16717-1-git-send-email-manjunath.b.patil@oracle.com
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>