msm: ipa3: fix compatibility with ipa_nat driver

Add several defines and structs to allow IPA nat driver compile.
Change IPA_HW_MAX to be a define instead of enum so user space
can check its existence with ifdef.

Change-Id: I33df449d18b678dca44475f04eb72318179dda11
Signed-off-by: Amir Levy <alevy@codeaurora.org>