ena: Remove \n from sysctl description

sysctl(8) prints a newline after the description, no need for this extra
newline.

MFC after: 1 week

(cherry picked from commit f2233ac33ab64f9bb03370c097af97f26dd0fca1)
(cherry picked from commit 1f6936723e1051e92fb9b658f5f6fa13c2001cee)