docs: bridge: add other features

Add some features that are not appropriate for the existing section to
the "Others" part of the bridge document.

Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>