Revert "RDS: Make message size limit compliant with spec"

Revert "RDS: Make message size limit compliant with spec"

This reverts commit ef278157f938011ee08fb683311e5e31ffd29fdf.

Orabug: 23217242

From Avinash Repaka <avinash.repaka@oracle.com>:
This patch reverts the fix for Orabug: 22661521, since the fix assumes
that the memory region is always aligned on a page boundary, causing an
EMSGSIZE error when trying to register 1MB region that isn't 4KB aligned.
These issues were observed on kernel 4.1.12-39.el6uek tag.

Signed-off-by: Avinash Repaka <avinash.repaka@oracle.com>
Acked-by: Chuck Anderson <chuck.anderson@oracle.com>