rmnet:Use platform independent API for 64-bit div

64-bit division( operator "/") on 32-bit platforms is not supported.
Using platform independent API's here.

Change-Id: I87207dfc2b4c0521e70b25642cdc29b84790d46c
Signed-off-by: Sharath Chandra Vurukala <sharathv@codeaurora.org>