rename libcommon to libgsupclient

All that is left in libcommon now are the GSUP and OAP client implementations.
These are duplicated in osmo-sgsn.git and make sense to remain somewhat
separate from libmsc. So now they get their own little lib.

Change-Id: Ic71aa119c233b6a0ae169a5b2a53819903d2be82
12 files changed