MFC: r317465

MFC: r317465
Fix handling of a NFSv4.1 callback reply from the session cache.

The nfsv4_seqsession() call returns NFSERR_REPLYFROMCACHE when it has a
reply in the session, due to a requestor retry. The code erroneously
assumed a return of 0 for this case. This patch fixes this and adds
a KASSERT(). This would be an extremely rare occurrence. It was found
during code inspection during the pNFS server development.

git-svn-id: svn://svn.freebsd.org/base/stable/10@318128 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f