nfs_commonkrpc.c: Fix recovery that was broken by 4d80d4913e79

Commit 4d80d4913e79 added a check for nfsess_defunct already
being set. This was incorrect because, once set, nfsess_defunct
remains set and an additional recovery might be needed.

This patch reverts this part of 4d80d4913e79.

PR: 297252
Suggested by: olivier
MFC after: 3 days
Fixes: 4d80d4913e79 ("nfs: Fix argument typo to avoid a crash")