Changes

scripts: osmo_git_clone_url: prefer using gerrit

Use gerrit as clone URL for libgtpnl, libasn1c, libsmpp34 and libusrp,
as the gitea URL for these is just a (very delayed!) mirror.

Related: https://osmocom.org/projects/cellular-infrastructure/wiki/Git_infrastructure
Change-Id: I6c643d31e1451d97566691b83a4167d42f3f5e41