MFC: r298495

MFC: r298495
Fix a LOR in the NFSv4.1 server.

The ordering of acquisition of the state and session mutexes was
reversed in two cases executed when an NFSv4.1 client created/freed
a session. Since clients will typically do this only when mounting
and dismounting, the likelyhood of causing a deadlock was low but possible.
This can only occur for NFSv4.1 mounts, since the others do not
use sessions.
This was detected while testing the pNFS server/client where the
client crashed during dismounting.
The patch also reorders the unlocks, although that isn't necessary
for correct operation.

git-svn-id: svn://svn.freebsd.org/base/stable/10@299222 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f