RDMA: Provide safe ib_alloc_device() function

All callers to ib_alloc_device() provide a larger size than struct
ib_device and rely on the fact that struct ib_device is embedded in their
driver specific structure as the first member.

Provide a safer variant of ib_alloc_device() that checks and enforces this
approach to make sure the drivers are using it right.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/sw/rdmavt/vt.c

@@ -91,7 +91,7 @@ struct rvt_dev_info *rvt_alloc_device(size_t size, int nports)
 {
 	struct rvt_dev_info *rdi;
 
-	rdi = (struct rvt_dev_info *)ib_alloc_device(size);
+	rdi = container_of(_ib_alloc_device(size), struct rvt_dev_info, ibdev);
 	if (!rdi)
 		return rdi;