Update packetfilter when peers change

Previously we did not update the packet filter
when nodes changed, which would cause new nodes
to be missing from packet filters of old nodes.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/types/machine.go

@@ -353,3 +353,13 @@ func (machines MachinesP) String() string {
 
 	return fmt.Sprintf("[ %s ](%d)", strings.Join(temp, ", "), len(temp))
 }
+
+func (machines Machines) IDMap() map[uint64]Machine {
+	ret := map[uint64]Machine{}
+
+	for _, machine := range machines {
+		ret[machine.ID] = machine
+	}
+
+	return ret
+}