This first implementation uses libgtp to manage the GTPv1-U socket and
pdp contexts, as a proof of concept to have something working for now.
At a later step, it is expected to drop libgtp and use some adhoc code
to handle GTP-U.
Related: SYS#5516
Change-Id: I5a6f5dfc4e508c92adb35210b4dc576d64353366
