libs: update jpnfs library

update to a bugfix relase of NFS code:

this fixes enforce security flavor in the export file.

Example entry in export file:

/some/export/path *(rw,sec=krb5)

Changelog for jpnfs-0.5.2..jpnfs-0.5.5
    * [178bddd] nfs: added support for sec flavor in export file
    * [91f4cba] vfs: check security flavor used by client
    * [2cd3029] nfsv3: reply correct auth flavor of mount
    * [ca91195] nfs: ignore and log export entries with unsupported options
    * [be6ff36] junit: refactor v4 test to reduce code duplication
    * [485b6a4] nfsv41: fix open stateid leak

Acked-by: Paul Millar
Target: master, 2.7, 2.6
Require-book: yes
Require-notes: yes
Merge pull request #162 from kofemann/2.6

libs: update jpnfs library