Depend on both libosmo-sigtran-dev and libosmo-sccp-dev

libmsc/a_iface.c and libmsc/a_iface_bssap.c still include
osmocom/sccp/sccp_types.h to get access to enums defining SCCP
cause values.  Until that is resolved, we have to keep the build
dependency to libosmo-sccp-dev

Change-Id: I957dcb2bcce216d0fd81a58bfe869aca0e4624a8
Related: OS#2601
diff --git a/debian/control b/debian/control
index c017e16..12d8364 100644
--- a/debian/control
+++ b/debian/control
@@ -15,6 +15,7 @@
                libsmpp34-dev,
                libasn1c-dev,
                libosmocore-dev,
+               libosmo-sccp-dev,
                libosmo-sigtran-dev,
                libosmo-abis-dev,
                libosmo-mgcp-client-dev,