Changes

Move xUA<->LM SAP logic to its own file

Right now it's difficult to gasp what's implemented of the SAP since it
was scattered around several places.
Put all the SAP forwarding logic into its own file so it's easy to
follow and extend (eg. adding new helper functions, etc.)

Change-Id: I93d74dd7f6ea8f2e60a8bc41be15362e433e8962