RFC: Dealing with an MFC to stable/13 that breaks the lobprocstat build

Hi,

So I did an MFC that broke the stable/13 build (it's reverted now).
I didn't realize that changes inside _KERNEL in mount.h would do
this, but now I know.

Since it is only an issue for stable/13 (and not main), I'd like to do a
minimal fix on the MFC and not mess with adding #includes to libprocstat
sources.

There are two of them:
1 - A prototype for a new function called vfs_exjail_delete(), which is in
     vfs_export.c and is called in kern_jail.c.
    --> For this one, I think the easiest fix is to just move the function
          prototype from mount.h to jail.h.

2 - Adding a "bool" argument to vfs_export().
     For this one, I think the easiest fix is to re-define the
argument as an "int"
     and pass it in as 0/1 instead of false/true.

Are others agreeable to these changes to the code for the MFS into stable/13?
(Not affecting main.)

rick