rxrpc: fix some null-ptr-deref bugs in server_key.c
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.15.33 by commit 432297011caf71dbc95c3365a65adf365e79aff3, it was introduced in version v5.11 by commit 12da59fcab5a05d01773e7cb413b8b8f3bb4e334. For more details please see the references link.