Preset the maximum file size before we get to nfs_fsinfo(), based on

Preset the maximum file size before we get to nfs_fsinfo(), based on
an (over?) conservative assumption about what the client can store in it's
buffer cache using a signed 32-bit 512-byte block number index.  Otherwise
it's possible for some file access when maxfilesize = 0 (eg: /usr is nfs
mounted and doing an execve())
Pointed out by:	 bde

XXX It might make sense to do a preemptive nfs_fsinfo() call at mount time.