libosmocore.spec: Make libosmocore-devel require libsctp

Now that the libosmo*.pc files 'Require' the libsctp pkg-config
file to be installed, we need an explicit package dependency
from libosmocore-devel to lksctp-tools-devel, the package providing
the related libsctp.pc file.

Change-Id: I967369f6726e88946872881d298ab90440ca2c0e
diff --git a/contrib/libosmocore.spec.in b/contrib/libosmocore.spec.in
index c2fe738..d699b58 100644
--- a/contrib/libosmocore.spec.in
+++ b/contrib/libosmocore.spec.in
@@ -129,6 +129,7 @@
 Group:          Development/Libraries/C and C++
 Requires:       libosmocore18 = %version
 Requires:       libtalloc-devel
+Requires:       lksctp-tools-devel
 
 %description -n libosmocore-devel
 libosmocore is a library with various utility functions shared