UNTESTED WIP: remove global bssgp_nsi variable

As we can now have several NS instances inside the program, let's
remove the global bsspg_nsi to which BSSGP bound itself.  Rather,
all functions are now parametrized based on the NS Instance that's
either
* explicitly passed to the function (in case no msgb and no bctx), or
* stated in the BVC context / bctx (if any), or
* explicitly given as argument to the function (if no msgb and no bctx)

Change-Id: Ibc7df60caf4adef690001536bd7a1293d866a1c2
6 files changed