rtsold: handle media LINK_UP to accelerate RS/RA

[bz]

Summary

If a link is not UP at boot time, e.g., a cable gets plugged in later,
rtsold will not send out an RS and we have to wait for the next
unsolicitated RA to get a default router, prefix information, etc.

Hook into rtsolds routing message callback handler and rather than
complicating logic, simply re-set the internal timer if we find a link
UP and RUNNING (based on the rtmsg), and let the rtsold state machine
do the work.

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I wrote this in response to D56927 but never tested it.
I would appreciate if someone could test/review.

XXX-BZ also, is there a reference in an RFC related to this which we can/should
mention about this case?

[pouria]

It helps, but not much. it might increase ifi->timer.tv_sec to PROBE_INTERVAL which is 60s.

usr.sbin/rtsold/rtsock.c

183

191

Why do we need IFF_RUNNING here?

194

After some debugging, I found out rtm_index is not same as ifm_index.

[bz]

In D58211#1335366, @pouria wrote:

It helps, but not much. it might increase ifi->timer.tv_sec to PROBE_INTERVAL which is 60s.

So just doing the timer update is not enough? I wonder how we get it into a "reset" state to start running like on startup then without massive fiddling?

usr.sbin/rtsold/rtsock.c

191

Because if the interface is not UP and RUNNING you cannot transmit and so it would defeat the purpose.

194

That is a very good catch!