libosmocore: Build a 0.5.3+ version and force rebuild

The behavior of the OSMO_MIN/OSMO_MAX has been fixed. Update
the library and force the rebuild.
diff --git a/conf/layer.conf b/conf/layer.conf
index f428ace..11f7089 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -9,4 +9,4 @@
 BBFILE_PATTERN_telephony := "^${LAYERDIR}/"
 BBFILE_PRIORITY_telephony = "5"
 
-META_TELEPHONY_OSMO_INC = "5"
+META_TELEPHONY_OSMO_INC = "6"