nfscl: Use NFSMNTP_DELEGISSUED in two more functions

Commit 5e5ca4c8fc53 added a NFSMNTP_DELEGISSUED flag to indicate when
a delegation has been issued to the mount. For the common case
where an NFSv4 server is not issuing delegations, this flag
can be checked to avoid acquisition of the NFSCLSTATEMUTEX.

This patch adds checks for NFSMNTP_DELEGISSUED being set
to two more functions.

This change appears to be performance neutral for a small number
of opens, but should reduce lock contention for a large number of opens
for the common case where server is not issuing delegations.

MFC after: 2 week