tipc: use kfree_sensitive() for session key material

tipc: use kfree_sensitive() for session key material

The rx->skey field contains a struct tipc_aead_key with GCM-AES
encryption keys used for TIPC cluster communication. Using plain
kfree() leaves this sensitive key material in freed memory pages
where it could potentially be recovered.

Switch to kfree_sensitive() to ensure the key material is zeroed
before the memory is freed.

Fixes: 1ef6f7c9390f ("tipc: add automatic session key exchange")
Signed-off-by: Daniel Hodges <hodgesd@meta.com>
Link: https://patch.msgid.link/20260131180114.2121438-1-hodgesd@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>