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
diff --git a/src/Makefile.am b/src/Makefile.am
index b03ee8c..32bd4d7 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -21,7 +21,7 @@
 
 # Libraries
 SUBDIRS = \
-	libcommon \
+	libgsupclient \
 	libvlr \
 	libmsc \
 	libcommon-cs \