Various fixes focused on xattr and system.* xattr namespace.
They are required to have usable ACLs managed via 9P
- 9P/xattr : bug fixed, assumption was made that xattr's
  value is a string. This prevented ACLs
   (content of system.posix_acl_access), which is a binary buffer,
   to be set properly.
- 9P/ACL: Hook added to deal properly with pseudo xattr "system.posix_acl_access"
- 9P/ACL: the protocol implements hooks to deal correctly with "system.posix_acl_access" pseudo xattr
- 9P/xattr : an ACL corner case (visible with FSAL_VFS and not FSAL_LUSTRE) was fixed.
- FSAL_VFS/xattr : code in xattrs.c has been hardened as 9P ACL support was backported to VFS
Post-rebase fixes
Fix 9P regression introduced with commit 875f30df5534932a06aa046beafa00ba8a4f4c4c

Signed-off-by: Philippe DENIEL <philippe.deniel@cea.fr>
Re-indentation
checkpatch on  9p_attach.c
SQUASH ME