libosmocore.pc.in: Append -lsctp to Libs.private

It will be used by the linker when linking statically against
libosmocore.

Change-Id: I797b970b22053432b243e4ef9f6b0458727fc608
diff --git a/libosmocore.pc.in b/libosmocore.pc.in
index ce82d4f..80f17c8 100644
--- a/libosmocore.pc.in
+++ b/libosmocore.pc.in
@@ -7,5 +7,5 @@
 Description: C Utility Library
 Version: @VERSION@
 Libs: -L${libdir} @TALLOC_LIBS@ -losmocore
-Libs.private: @PTHREAD_LIBS@
+Libs.private: @PTHREAD_LIBS@ @LIBSCTP_LIBS@
 Cflags: -I${includedir}/ @TALLOC_CFLAGS@ @PTHREAD_CFLAGS@