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

Hi,

Please consider the attached for inclusion in the 5.0 queue. The justification should be apparent from reading the referenced bugzilla report. The upstream commit is 40ba1d9b4d19796afc9b7ece872f5f3e8f5e2c13 but I have attached the patch that was originally posted by Pablo because it can be applied to 5.0 without fuzz.