msm: ipa: rmnet_ipa: unify global variables to a context

This change creates a context variable to be allocated on heap
instead of multiple global variables. Having a single context makes
it easier to see the state of rmnet_ipa in crashdumps.

Change-Id: I3addae5ae984f708ee0d72e44ce993b35d4b2be0
CRs-Fixed: 968049
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>