jaildesc: remove file-mode-based access controls

Jail descriptors were given a file-like mode, user, and group, for the
purpose of controlling how the descriptor may be used.  This is too far
removed from the file paradigm to make sense.  Remove it in favor of a
better access control method to be added, such as Capsicum.

Also add missing code in jaildesc_fill_kinfo.

Reported by:	crest at rlwinm.de, kib
MFC after:	3 days

lib/libsys/jail.2

@@ -340,31 +340,6 @@ work the same as
 and
 .Fn jail_remove ,
 except that they operate on the jail referred to by the passed descriptor.
-.Pp
-Jail operations via descriptors can be done by processes that do not
-normally have permission to see or affect the jail,
-as long as they are allowed by the file permissions of the jail
-descriptor itself.
-These permissions can be changed by the descriptor owner via
-.Xr fchmod 2
-and
-.Xr fchown 2 .
-.Fn jail_get
-requires read permission,
-.Fn jail_set
-and
-.Fn jail_remove
-require write permission,
-and
-.Fn jail_attach
-requires execute permission.
-Also, use of a descriptor with the
-.Dv JAIL_AT_DESC
-flag requires execute permission.
-An owning descriptor is identified by the
-.Em sticky bit ,
-which may also be changed via
-.Xr fchmod 2 .
 .Sh RETURN VALUES
 If successful,
 .Fn jail ,
@@ -402,22 +377,6 @@ The
 system call
 will fail if:
 .Bl -tag -width Er
-.It Bq Er EACCES
-Write permission is denied on the jail descriptor in the
-.Va desc
-parameter,
-and the
-.Dv JAIL_USE_DESC
-flag was set.
-.It Bq Er EACCES
-Execute permission is denied on the jail descriptor in the
-.Va desc
-parameter,
-and either the
-.Dv JAIL_AT_DESC
-or
-.Dv JAIL_ATTACH
-flag was set.
 .It Bq Er EPERM
 This process is not allowed to create a jail, either because it is not
 the super-user, or because it would exceed the jail's
@@ -505,24 +464,6 @@ The
 system call
 will fail if:
 .Bl -tag -width Er
-.It Bq Er EACCES
-Read permission is denied on the jail descriptor in the
-.Va desc
-parameter,
-and the
-.Dv JAIL_USE_DESC
-flag was set.
-.It Bq Er EACCES
-Execute permission is denied on the jail descriptor in the
-.Va desc
-parameter,
-and the
-.Dv JAIL_AT_DESC
-flag was set.
-.It Bq Er EFAULT
-.Fa Iov ,
-or one of the addresses contained within it,
-points to an address outside the allocated address space of the process.
 .It Bq Er ENOENT
 The jail referred to by a
 .Va jid
@@ -597,14 +538,6 @@ will fail if:
 The
 .Fa fd
 argument is not a valid jail descriptor.
-.It Bq Er EACCES
-Permission is denied on the jail descriptor
-.Po
-execute permission for
-.Fn jail_attach_fd ,
-or write permission for
-.Fn jail_remove_fd
-.Pc .
 .It Bq Er EPERM
 The jail descriptor was created by a user other than the super-user.
 .It Bq Er EINVAL