nfscl: Enable detection of bad session slots

To deal with broken session slots caused by the use of the
"soft" and/or "intr" mount options, nfsv4_sequencelookup()
has been modified to track the potentially broken session
slots (commit 40ada74ee1da). Then, when all session slots
are potentially broken, nfsv4_sequencelookup() does a
DeleteSession operation, so that the NFSv4.1/4.2 server will
reply NFSERR_BADSESSION to uses of the session.
The client will then recover by doing a CreateSession to
acquire a new session.

This patch adds the code that marks potentially bad
slots, so that the above semantics become functional.
It has been successfully tested against a FreeBSD
NFSv4.1/4.2 server, but does not work against a Linux 5.15
NFSv4.1/4.2 server. (The Linux 5.15 server creates
a new session with the same sessionid as the destroyed
one and, as such, keeps returning NFSERR_BADSESSION.
I believe this is a bug in the Linux server.)

However, this should not cause a regression and will
make "intr" mounts fairly usable against the NFSv4.1/4.2
servers where it works.

PR: 260011
MFC after: 2 weeks