fix msgb talloc context initialization

Properly initialize msgb talloc context in hnbgw and all tests, using the new
msgb_talloc_ctx_init().

test-ranap.c: since msgb talloc ctx is now in test_common_init(), remove msgb
talloc init here.

Change-Id: I807c799aff1239184728551ed77fdafa73bd683f
diff --git a/src/tests/test-ranap.ok b/src/tests/test-ranap.ok
index 2ad19e6..bda3c8e 100644
--- a/src/tests/test-ranap.ok
+++ b/src/tests/test-ranap.ok
@@ -214,5 +214,5 @@
 00 0a 00 11 00 00 01 00 29 40 0a 00 00 01 00 28 40 03 05 c2 d0 
 report
 talloc report on 'asn1_context' (total      0 bytes in   1 blocks)
-talloc report on 'msgb' (total      1 bytes in   1 blocks)
+talloc report on 'msgb' (total      0 bytes in   1 blocks)
 exit