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

(cherry picked from commit 5ab48fb9f7ac43fb1242a678312a02df5d4d5b53)