bridge.4: Remove incorrect line + polish

In an AMA on Community Discord, it was revealed that simply setting a
bridge to up is not equivelant to setting it as "inet6 auto_linklocal".
Remove the incorrect line, and while here:

+ reset sysctl list width to indent, saving 2/13 lines on MANWIDTH 59/80
+ tag spdx + break two long lines over 80 characters

MFC after: 3 days
Reported by: Antranig Vartanian <antranigv@freebsd.am>
Reported by: Jan Bramkamp <crest+freebsd@rlwinm.de>
Reported by: Niclas <buero28@icloud.com>
Approved by: mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D48981