rxgkTime is 100s of nanoseconds, not microseconds

Bugs dating from january, sigh.

Change-Id: I69274d353f32bd76d74bc40bd1bb156c27aa8a35
Add some GSS service-specific bits

A new key to hold the GSS service-specific data and a routine to
set them.

Change-Id: I5bbae94840a2ee79c4e0503bf42751b6e122b677
Use rxgk_set_gss_specific in rxgkd

Nothing actually consumes the service-specific data that it sets,
yet, but have it ready for when we do.

Change-Id: I2e5eb3fe71df1f21482b1bd214bcc58319654c58
Make get_creds fetch from service-specific data

This changes its contract a bit, but should be more efficient.
Also means less hardcoding of values.

Change-Id: Ic737a050196584a9534d136302f27ec686875f06