RAN_Emulation: Modularize protocol support

The RAN_Emulation currently unconditionally provides BSSAP and MGCP support.
Let's re-structure the code so that support for those protocols is now
possible to enable/disable at compile time.

This patch is in preparation of introducing RANAP support in RAN_Emulation.

Change-Id: Id53ba3ff05f9946230e0e4a759245de14a0f9fbd
Related: OS#2856
12 files changed