Declare osmo_ctx_init() in talloc.h

This function is called automatically on the main thread, but needs to
ba called explicitly in order to run the select loop on another thread.
Make it available for applications through talloc.h

Change-Id: Ie710ca9ad01d3fadb9f4ff344a55d6c01004727b
diff --git a/include/osmocom/core/talloc.h b/include/osmocom/core/talloc.h
index c68a56c..f15cd2a 100644
--- a/include/osmocom/core/talloc.h
+++ b/include/osmocom/core/talloc.h
@@ -25,3 +25,5 @@
  * to the various _c functions like msgb_alloc_c() */
 #define OTC_GLOBAL (osmo_ctx->global)
 #define OTC_SELECT (osmo_ctx->select)
+
+int osmo_ctx_init(const char *id);