NFS mount inside jail fails

[Sean Bruno]

Silly thing I ran into today.  User wanted to NFS mount a dir inside a
jail.  After I groaned about the security implication of this, I noted
that there is a sysctl that looks like it should allow this.  Namely,
security.jail.mount_allowed.  I noted that setting this follows a path
that *should* have allowed this silly thing to happen, except that the
credentials in the nfsclient were not setup correctly.

e.g.  VFS_SET(nfs_vfsops, oldnfs, VFCF_NETWORK);
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I changed this to:
VFS_SET(nfs_vfsops, oldnfs, VFCF_NETWORK|VFCF_JAIL);

This seems to allow the user's desired effect after setting
security.jail.mount_allowed=1

I *think* this is the correct behavior, if a bit silly when taking into
account the purpose of a jail.

Thoughts?

Sean