New option to tune startup delay

[Bischoff]

This pull request introduces a new option to mrouted daemon

--startup-delay=DELAY

or

-D DELAY

that defaults to 10 seconds and that enables to set up the previously hardcoded to 10 seconds delay before applying the new routes.

I tested it with a very simple setup host -- router -- host where both hosts try to join the same multicast group. It has not been tested with more complicated setups, with several routers, where DVMRP protocol would start playing its role.

However, with this simple setup, it proved to work, even when setting the delay to 0 (which is equivalent to disabling the wait phase at startup): the router immediately applies the routes it got from IGMP.

[troglobit]

Yeah this is much better than what I proposed yesterday. Dunno what I was smoking ...