Fix a bug in mbuf_free_bulk() (#36)
Fix a bug in mbuf_free_bulk() (#36)

mbuf_free_bulk() always failed thus always slow path was used.
The problem was threefold:
1. mbuf_ptrs was not correctly set
   (pointer addresses were not used directly, but dereferenced)
2. mbuf_ptrs and buf_addrs_actual have different orderings
3. the size of metadata slots (128 bytes) was not accounted.
NetSys/e2d2,apanda/NetBricks,NetSys/e2d2,NetSys/NetBricks,apanda/NetBricks,NetSys/NetBricks,NetSys/e2d2,NetSys/e2d2,NetSys/NetBricks,NetSys/e2d2,NetSys/NetBricks,apanda/NetBricks,NetSys/NetBricks,apanda/NetBricks,NetSys/e2d2,NetSys/e2d2,apanda/NetBricks