Use UID as requestID

This change makes all requestIDs use the UID of the creator, ensuring
that rekeys always use the same requestID. This also has the nice
property of separating app's resources from each other, and allowing for
identification of which app/UID allocated the resources from
command-line dumps (eg ip xfrm state show)

Bug: 111841561
Test: Updated tests & passing taimen
Change-Id: I4f1eadcdb795766ae4682b15e41727359c52fa38