BSSGP_Emulation: Support multiple PTP-BVC within one Entity

The existing BSSGP_Emulation is built around the assumption that every
instance of BSSGP_Emulation only servers one signaling-BVC and one
PTP-BVC.  While this is true for osmo-pcu at this point (BTS-colocated
PCU), other BSS/PCU implementations differ.

In general, there can always be any number of PTP BVC (one per cell)
next to the signaling BVC (one per BSS).  Let's represent this in
BSSGP_Emulation so we can create more comprehensive tests.

Change-Id: I7e30b4c4e188518a574e082962fba457b3a97ce3
8 files changed