netfilter: nf_tables: pass context to nft_set_destroy()

commit 0c2a85ed upstream.

The patch that adds support for stateful expressions in set definitions
require this.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>