RDS: IB: restore the vector spreading for the CQs

RDS: IB: restore the vector spreading for the CQs

Since the IB_CQ_LEAST_LOADED vector support is not their on newer
kernels(post OFED 1.5), we had #if 0 code for it which got removed
as part of 'commit 3f1db626594e ("RDS: IB: drop discontinued IB
CQ_VECTOR support")'. On UEK2, the drivers had implementation
for this IB verb. UEK4 which is based on newer kernel obviously
doesn't support it.

RDS had an alternate fallback scheme which can be used in absence
of the dropped verb. On UEK2, we didn't use it but UEK4 RDS code was
silently using that till the code got removed. The patch restores
that code with bit more clarity on what it is actually doing.

Orabug: 23550561

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>