fortuna: Deduplicate kernel vs user includes

No functional change.

Reviewed by: markj, markm
Approved by: secteam (delphij), core (brooks)
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D19409
(cherry picked from commit e66ccbeaa3613d022dbc07b9f7403c6bfbe40be6)