Pull request #4205: sfip: set pointers to nullptr after deletion to avoid heap-use...

Pull request #4205: sfip: set pointers to nullptr after deletion to avoid heap-use-after-free on reload

Merge in SNORT/snort3 from ~MMATIRKO/snort3:sfvar_mem to master

Squashed commit of the following:

commit 43ffbe3a7b41e0fd6198cf51444955ce6ea057c4
Author: Michael Matirko <mmatirko@cisco.com>
Date:   Wed Feb 14 16:36:53 2024 -0500

    sfip: remove references to unused mode feature

commit 81cabc672c4196bae2a56c112641c5a9807667bf
Author: Michael Matirko <mmatirko@cisco.com>
Date:   Tue Feb 13 16:34:46 2024 -0500

    sfip: zero out var/node pointers after operations to remedy heap-use-after-free on reload