RDS: IB: scale rds_ib_allocation based on fragment size

RDS: IB: scale rds_ib_allocation based on fragment size

The 'rds_ib_sysctl_max_recv_allocation' allocation is used to manage
and allocate the size of IB receive queue entry (RQE) for each IB
connection. However, it relies on the hardcoded RDS_FRAG_SIZE.

Lets make it scalable based on supported fragment sizes for different
IB connection. Each connection can allocate different RQE size
depending on the per connection fragment_size.

Orabug: 21894138
Reviewed-by: Wei Lin Guay <wei.lin.guay@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>