bridge.4: Remove incorrect line + polish

[ziaee]

Summary

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 <[e-mail]>
Reported by: Jan Bramkamp <[e-mail]>
Reported by: Niclas <[e-mail]>