fusefrontend_reverse: switch to stable inode numbers

The volatile inode numbers that we used before cause "find" to complain and error out.
Virtual inode numbers are derived from their parent file inode number by adding 10^19,
which is hopefully large enough no never cause problems in practice.

If the backing directory contains inode numbers higher than that, stat() on these files
will return EOVERFLOW.

Example directory lising after this change:

  $ ls -i
               926473 gocryptfs.conf
  1000000000000926466 gocryptfs.diriv
               944878 gocryptfs.longname.hmZojMqC6ns47eyVxLlH2ailKjN9bxfosi3C-FR8mjA
  1000000000000944878 gocryptfs.longname.hmZojMqC6ns47eyVxLlH2ailKjN9bxfosi3C-FR8mjA.name
               934408 Tdfbf02CKsTaGVYnAsSypA

0 files changed, 0 insertions, 0 deletions