Allocate memory for the btable structure

In vr_btable_attach, for the btable metadata, we allocate memory
only for a pointer, while end up using that memory as a structure.
Hence, allocate memory for the whole structrure rather than for
the pointer to the structure.

Change-Id: Iccf2793a6c3bcac06aed9cfe2011e9364e1f9397
Closes-Bug: #1678704

dp-core/vr_btable.c

@@ -181,7 +181,7 @@ vr_btable_attach(struct iovec *iov, unsigned int iov_len,
     if (iov[0].iov_len % esize)
         return NULL;
 
-    alloc_size = sizeof(struct vr_btable *);
+    alloc_size = sizeof(struct vr_btable);
     alloc_size += (sizeof(void *) * iov_len);
     alloc_size += (sizeof(struct vr_btable_partition) * iov_len);