libs: update nfs library

bugfix version:

Changelog for nfs4j-0.6.2..nfs4j-0.6.3
    * [ebf7974] nfsv3: fix hard link creation (similar to http://rb.dcache.org/r/6224)

Acked-by: Paul Millar
Target: master, 2.7, 2.6
Require-book: no
Require-notes: no
(cherry picked from commit ccd9cb105fcd7be8590f89e19438c684870b69a0)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #318 from kofemann/update-nfs-2.7

libs: update nfs library