ospf6d: extend the "redistribute" command with more options

ospf6d: extend the "redistribute" command with more options

Add the "metric" and "metric-type" options to the "redistribute"
command.

This is a small commit since the logic of setting the metric
value and type of external routes was already present due to the
implementation of the "default-information originate" command months
ago. This commit merely extends the "redistribute" command to
leverage that functionality.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>