arswitch.4: Improve title and add HARDWARE

For visibility in apropos and inclusion in the hardware release notes.

MFC after: 3 days
Reviewed by: adrian (previous), mhorne
Approved by: mhorne (mentor)
Approved by: re (cperciva)
Differential Revision: https://reviews.freebsd.org/D50322

(cherry picked from commit 9692d5e15e9bd7e628b06d655522477ce8c5b6fe)
(cherry picked from commit 1343a5b616ec4e11047c5024bb844e7275f84ddd)