Bugfix: Used&reserved addresses are counted twice

When reserved addresses are in use, unused_count would subtract them
twice.
Fixes #440.

mreg/api/v1/tests/test_networks.py

@@ -525,6 +525,9 @@ def test_reject_ip_usage(self):
     def test_count_unused_ips(self):
         """Test that excluded ipaddresses are exempted from the unused count"""
         self.test_create()
+        # Create a host that uses one of the reserved addresses. (Should not be counted twice)
+        host1 = Host.objects.create(name='host1.example.org')
+        Ipaddress.objects.create(host=host1, ipaddress='10.0.0.2')
         ret = self.assert_get(f'/api/v1/networks/{self.network4}/unused_count').json()
         # /24 - net/broadcast - reserved - [10, 200] - 201
         # 256 - 2             - 3        - 191       - 1   = 59

mreg/models.py

@@ -609,10 +609,9 @@ def unused_count(self):
         # subtract excluded ranges
         for i in self.excluded_ranges.all():
             result -= i.num_addresses()
-        # subtract reserved addresses
-        result -= len(self.get_reserved_ipaddresses())
-        # subtract used addresses
-        result -= len(self.used_addresses)
+        # subtract used and reserved addresses
+        used_or_reserved = self.used_addresses | self.get_reserved_ipaddresses()
+        result -= len(used_or_reserved)
         return result
 
     def get_first_unused(self):