Add missing file to sys/conf/files after 469884cf04a9b92677c7c83e229ca6b8814f8b0a .

Found by: vishwin@
Differential Revision: https://reviews.freebsd.org/D29921
MFC after: 1 week
Sponsored by: NVIDIA Networking

(cherry picked from commit 9340ebd404efad7068b5a45fd3b3d8bb21187b91)