[44net] amprgw routing

I've made some changes to the amprgw routing mechanism.

Replacing the earlier sequential search through the routing table with a binary search has significantly sped up lookups, which can happen up to twice per packet forwarded (once for source address, once for destination address).

Three times an hour, a background process fetches the encap routing table from the portal, and if it has changed, signals the router process to update its routing table. The routing table update seems to take about 3 msec during which packets can't be looked up and so are not forwarded.

This fetch also updates the data source for the rip sender, so you'll receive updates more quickly now. - Brian