nfscl: Fix CreateSession for an established ClientID

Commit 981ef32230b2 added optional use of the session
slots marked bad to recover a new session when all
slots are marked bad. The recovery worked against
a FreeBSD NFSv4.1/4.2 server, but not a Linux one.
It turns out that it was a bug in the FreeBSD client
and not the Linux server.

This patch fixes the client so that DeleteSession
followed by CreateSession after receiving a
NFSERR_BADSESSION error reply works against the
Linux server (and conforms to the RFC).

This also implies that the FreeBSD NFSv4.1/4.2
server needs to be fixed in a future commit.
Without the fix, the FreeBSD server does a full
recovery, including creation of a new ClientID,
but since "intr" mounts were broken, this does
not result in a regression.

This patch only affects the case where a CreateSession
is done for an already confirmed ClientID, which was
not being done prior to commit 981ef32230b2.

PR: 260011
MFC after: 2 weeks