Changes

ttcn3-gbproxy-test-fr: depend also on osmo-sgsn-master

osmo-gbproxy-master is derived from osmo-sgsn-mater, and the former
needs to be re-built to catch up with osmo-sgsn.git changes (Where
the osmo-gbproxy source code is located)

Change-Id: I8abc9f89d19d657403569b7705cd923342ff300b