msm: ipa: define newly added pure_ack FnR equation

New IPA Filtering and Routing equation, called
is_pure_ack, is supported by the IPA H/W.
This change enables common user space modules
to compile successfully with different kernels.

CRs-Fixed: 2334239
Change-Id: I66d7e34990afdfd69094159975ee9d5bf0f60340
Signed-off-by: Ghanim Fodi <gfodi@codeaurora.org>