namei: Abstract out OGM functions a bit more

namei: Abstract out OGM functions a bit more

Add GetWinOGM and SetWinOGM for getting and setting the
Windows-equivalent of the Unix OGM data. Make those and CheckOGM use
GetFileTime/SetFileTime so we can operate just via an FD_t, without
needing the full pathname. Modify the NT namei_icreate to use
SetWinOGM.

Change-Id: I5077911d8473d44ad9ba1d17d3b6deec3a12ba39
Reviewed-on: http://gerrit.openafs.org/6945
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>