support keyrings for NFS TLS mounts v2

Christoph Hellwig
2025-05-15T11:51:11Z

Hi all,

this series allows storing the key and certificate for NFS over
TLS mounts in the keyring and be specified using a mount option.
This way they don't need to be hardcoded in the global tlshd.conf
configuration file and can even be different per-mount.

Note that for now the .nfs keyring still needs to be added to
tlshd.conf, but that should go away with the handshake enhacement
from Hannes.

Changes since v1:
- don't depend on nfsv4 for the keyring
- fix compile when the kernel keyring is disabled