IB/uverbs: Use uverbs_api to manage the object type inside the uobject

Currently the struct uverbs_obj_type stored in the ib_uobject is part of
the .rodata segment of the module that defines the object. This is a
problem if drivers define new uapi objects as we will be left with a
dangling pointer after device disassociation.

Switch the uverbs_obj_type for struct uverbs_api_object, which is
allocated memory that is part of the uverbs_api and is guaranteed to
always exist. Further this moves the 'type_class' into this memory which
means access to the IDR/FD function pointers is also guaranteed. Drivers
cannot define new types.

This makes it safe to continue to use all uobjects, including driver
defined ones, after disassociation.

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

include/rdma/ib_verbs.h

@@ -1524,7 +1524,7 @@ struct ib_uobject {
 	atomic_t		usecnt;		/* protects exclusive access */
 	struct rcu_head		rcu;		/* kfree_rcu() overhead */
 
-	const struct uverbs_obj_type *type;
+	const struct uverbs_api_object *uapi_object;
 };
 
 struct ib_udata {