netfilter: nf_tables: fix memory leak during stateful obj update

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: fix memory leak during stateful obj update stateful objects can be updated from the control plane. The transaction logic allocates a temporary object for this purpose. The ->init function was called for this object, so plain kfree() leaks resources. We must call ->destroy function of the object. nft_obj_destroy does this, but it also decrements the module refcount, but the update path doesn't increment it. To avoid special-casing the update object release, do module_get for the update case too and release it via nft_obj_destroy().