When a NFSv4.1/4.2 session to the NFS server (not a pNFS DS) is
replaced, the old session should always be marked defunct by
nfsess_defunct being set non-zero.

However, the hang reported by the PR suggests that this might
be the case.

This patch adds a printf() to indicate this has somehow happened.

PR:	260011
MFC after: 	2 weeks