[PATCH] keys: prevent slab cache merging for key_jar

[Mohammed EL Kadiri]

Hi Jarkko, Vlastimil,

I will send a v2 this evening with the commit message reworked. I will
remove CVE references and frame it as hardening rather than an active
vulnerability. I'll also drop the inaccurate skbuff_head_cache
comparison that Vlastimil flagged.

No need to strip it yourself, I'll have it out today.

Thanks,
Mohammed