timespec: Add timespec_add_nsec helper

Add a (timespec) = (timespec) + (nsec) helper, to save intermediate
conversions to nanoseconds in its users.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
3 files changed