move msgb talloc context into talloc_ctx.c

This keeps the ordering right, independent of link ordering, it
will ensure that the talloc dump will also catch msgb related
memory leaks.
diff --git a/openbsc/src/talloc_ctx.c b/openbsc/src/talloc_ctx.c
index aa9f0b4..e90677b 100644
--- a/openbsc/src/talloc_ctx.c
+++ b/openbsc/src/talloc_ctx.c
@@ -1,6 +1,7 @@
 #include <openbsc/talloc.h>
 #include <openbsc/gsm_data.h>
 
+extern void *tall_msgb_ctx;
 extern void *tall_fle_ctx;
 extern void *tall_locop_ctx;
 extern void *tall_gsms_ctx;
@@ -16,6 +17,7 @@
 
 void talloc_ctx_init(void)
 {
+	tall_msgb_ctx = talloc_named_const(tall_bsc_ctx, 0, "msgb");
 	tall_fle_ctx = talloc_named_const(tall_bsc_ctx, 0, 
 					  "bs11_file_list_entry");
 	tall_locop_ctx = talloc_named_const(tall_bsc_ctx, 0, "loc_updating_oper");