[sccp] Implement parts of ITU SCCP for use in the A-Interface

include/sccp/sccp_types.h contain Q.713 and GSM definitions
include/sccp/sccp.h is the application interface resembling
                    the esentials of the UNIX socket interface.

src/sccp.c is the actual implementation of SCCP featuring
           connection and UDT1 support.

tests/sccp/sccp.c is testing connection creation and formating
                  of the SCCP messages used by the A-interface. And
                  it contains a simple fuzzing test to test the
                  robustnes of the implementation.
diff --git a/openbsc/tests/Makefile.am b/openbsc/tests/Makefile.am
index 2d4e81c..f40105f 100644
--- a/openbsc/tests/Makefile.am
+++ b/openbsc/tests/Makefile.am
@@ -1 +1 @@
-SUBDIRS = debug timer sms gsm0408 db channel
+SUBDIRS = debug timer sms gsm0408 db channel sccp