bumping mount path lengths in struct statfs

[Will Andrews]

Hi,

struct statfs contains the following:

 90         char      f_mntfromname[MNAMELEN];  /* mounted filesystem */
 91         char      f_mntonname[MNAMELEN];    /* directory on which mounted */

Where MNAMELEN is, currently, 88.  These limit the length of the path
that a filesystem can be mounted to.  This is enforced by
kern/vfs_mount.c:vfs_donmount().  This limit seems archaic, especially
given use cases like virtualization (large filesystem structures to
support underlying VMs), builds (which often make extensive use of
chroot with nullfs/NFS), ZFS, snapshots, etc.  Does anyone object to
bumping MNAMELEN to 1024 (PATH_MAX/MAXPATHLEN)?  Or some other
reasonably large value?

--Will.