Add "mountcritremote" to the REQUIRE line for nfsd.

For a pNFS MDS server, there must be mounts done to the DSs before the
nfsd is started. Adding the REQUIRE line makes sure these are done.
If there are NFS mounts in /etc/fstab that cannot be completed before
the nfsd starts, the "bg" mount option can still be used to handle that.
I do not believe this should cause problems for non-pNFS NFS servers.
(I have requested a review by rc@, but it is still pending.)