Use proposed experimental 2.4 packages

diff --git a/shibboleth/sp b/shibboleth/sp
index e3ee921..c7caa6c 160000 (submodule)
--- a/shibboleth/sp
+++ b/shibboleth/sp
@@ -1 +1 @@
-Subproject commit e3ee921ca75f1f0b9b5909d8bb5f91347a022a9c
+Subproject commit c7caa6c5650795c99dd9303fdc53e164e9f0a525