use Space.NumFreeAddresses for calculating transferred ip count

...rather than Space.NumFreeAddressesInRange; we don't care about the
universe.

Alternatively we could make Space.AddRanges return the count. But
AddRanges doesn't know whether the ranges overlap with existing free
space - that is only guaranteed by the context - so would have to do
much the same before/after calculation.

Another alternative would be to add the range sizes in
AdminTakeoverRanges. But that is more code and less clear.

ipam/allocator.go

@@ -403,9 +403,9 @@ func (alloc *Allocator) AdminTakeoverRanges(peerNameOrNickname string) address.C
 			return
 		}
 
-		before := alloc.space.NumFreeAddressesInRange(alloc.universe)
+		before := alloc.space.NumFreeAddresses()
 		alloc.space.AddRanges(newRanges)
-		after := alloc.space.NumFreeAddressesInRange(alloc.universe)
+		after := alloc.space.NumFreeAddresses()
 
 		alloc.gossip.GossipBroadcast(alloc.Gossip())
 

ipam/space/space.go

@@ -88,6 +88,14 @@ func (s *Space) Claim(addr address.Address) error {
 	return nil
 }
 
+func (s *Space) NumFreeAddresses() address.Count {
+	res := address.Count(0)
+	for i := 0; i < len(s.free); i += 2 {
+		res += address.Length(s.free[i+1], s.free[i])
+	}
+	return res
+}
+
 func (s *Space) NumFreeAddressesInRange(r address.Range) address.Count {
 	res := address.Count(0)
 	s.walkFree(r, func(chunk address.Range) bool {

ipam/space/space_test.go

@@ -19,16 +19,6 @@ func ip(s string) address.Address {
 	return addr
 }
 
-// Helper function to avoid 'NumFreeAddressesInRange(start, end)'
-// dozens of times in tests
-func (s *Space) NumFreeAddresses() address.Count {
-	res := address.Count(0)
-	for i := 0; i < len(s.free); i += 2 {
-		res += address.Length(s.free[i+1], s.free[i])
-	}
-	return res
-}
-
 func TestLowlevel(t *testing.T) {
 	a := []address.Address{}
 	a = add(a, 100, 200)