netfilter: nf_tables: fix set double-free in abort path

[Pablo Neira Ayuso]

Hi Greg,

I'm receiving several emails for a bit of time now to request to
cherry-pick this patch:

        40ba1d9b4d19 netfilter: nf_tables: fix set double-free in abort path

to kernel 5.0 stable queue. I'd appreciate if you can do so.

Thanks!