libosmocore.pc.in: put libsctp in Requires.private

The libsctp use in libosmocore is internal, not exposed to applications.
Hence, it must not be in "Requires" but in "Requires.private".

Fixes: 12eed19066a11aece6f346b54b85326bc6ba7f0b
Change-Id: Ic3e4e191990e6b76ec52b81e506b49980e20ce20
diff --git a/libosmocore.pc.in b/libosmocore.pc.in
index 3bb9b9a..6296417 100644
--- a/libosmocore.pc.in
+++ b/libosmocore.pc.in
@@ -6,7 +6,8 @@
 Name: Osmocom Core Library
 Description: C Utility Library
 Version: @VERSION@
-Requires: talloc, libsctp
+Requires: talloc
+Requires.private: libsctp
 Libs: -L${libdir} -losmocore
 Libs.private: @PTHREAD_LIBS@
 Cflags: -I${includedir}/ @PTHREAD_CFLAGS@