CVE-2023-52581: Missing Release of Memory after Effective Lifetime

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_tables: fix memleak when more than 255 elements expired

When more than 255 elements expired we're supposed to switch to a new gc container structure.

This never happens: u8 type will wrap before reaching the boundary and nft_trans_gc_space() always returns true.

This means we recycle the initial gc container structure and lose track of the elements that came before.

While at it, don't deref 'gc' after we've passed it to call_rcu.