nfscl: Use Claim_Null_FH and Claim_Deleg_Cur_FH

For NFSv4.1/4.2, there are two new options for the Open operation.
These two options use the file handle for the file instead of the
file handle for the directory plus a file name. By doing so, the
client code is simplified (it no longer needs the "nfsv4node" structure
attached to the NFS vnode). It also avoids problems caused by another
NFS client (or process running locally in the NFS server) doing a
rename or remove of the file name between the Lookup and Open.

Unfortunately, there was a bug (fixed recently by commit X)
in the NFS server which mis-parsed the Claim_Deleg_Cur_FH
arguments. To allow this patch to work with the broken FreeBSD
NFSv4.1/4.2 server, NFSMNTP_BUGGYFBSDSRV is defined and is set
when a correctly formatted Claim_Deleg_Cur_FH fails with NFSERR_EXPIRED.
(This is what the old, broken NFS server does, since it erroneously
uses the Getattr arguments as a stateID.) Once this flag is set,
the client fills in a stateID, to make the broken NFS server happy.

Tested at a recent IETF NFSv4 Bakeathon.

MFC after: 1 month