Don't throw away Open state when a NFSv4.1 client recovery fails.

If the ExchangeID/CreateSession operations done by an NFSv4.1 client
after the server crashes/reboots fails, it is possible that some process/thread
is waiting for an open_owner lock. If the client state is free'd, this
can cause a crash.
This would not normally happen, but has been observed on a mount of the
AmazonEFS service.

Reported by: cperciva
Tested by: cperciva
PR: 216086
MFC after: 2 weeks