nvme-keyring: restrict match length for version '1' identifiers

TP8018 introduced a new TLS PSK identifier version (version 1), which appended
a PSK hash value to the existing identifier (cf NVMe TCP specification v1.1,
section 3.6.1.3 'TLS PSK and PSK Identity Derivation').
An original (version 0) identifier has the form:

NVMe0<type><hmac> <hostnqn> <subsysnqn>

and a version 1 identifier has the form:

NVMe1<type><hmac> <hostnqn> <subsysnqn> <hash>

This patch modifies the lookup algorthm to compare only the first part
of the identifier (excluding the hash value) to handle both version 0 and
version 1 identifiers.
And the spec declares 'version 0' identifiers obsolete, so the lookup
algorithm is modified to prever v1 identifiers.

Signed-off-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>