Fix msgb_test on 64 bit architectures

truncating the unsigned long pointer msg->data to 'int' and then passin
git into msgb_resize_area() is unsafe as depending on the 32rd address
bit it will be eiether negative or positive.  That will in turn change
the expected "Sub area is not fully contained in the msg data\n" error
message into "Negative sizes are not allowed\n" which is not what the
autotest case expects.

Change-Id: I87ce13c265704d4ba8724e7dc7ed874c1128e0fa
diff --git a/tests/msgb/msgb_test.c b/tests/msgb/msgb_test.c
index a726ef4..ac10382 100644
--- a/tests/msgb/msgb_test.c
+++ b/tests/msgb/msgb_test.c
@@ -195,7 +195,7 @@
 	OSMO_ASSERT(e != 0);
 
 	if (OSMO_PANIC_TRY(&e))
-		msgb_resize_area(msg, NULL, (int)msg->data, 0);
+		msgb_resize_area(msg, NULL, 0, 0);
 	OSMO_ASSERT(e != 0);
 
 	if (OSMO_PANIC_TRY(&e))