fix: stop deriving NAT translations from IPv6 pinholes

Closes netork#116.

`get_port_forwards` reports IPv4 mappings and IPv6 pinholes together, which is
right — both are inbound rules someone configured. `get_nat_translations` then
iterated all of them, and that is not: a pinhole is a firewall hole, and IPv6
does not do NAT at all.

The entries it produced were nonsense in two ways. They paired an IPv6 host with
the IPv4 WAN address, and `inside_local` came out as "2001:db8::10:22", where
the last colon is a port separator and everything before it is an address that
also contains colons.

The two failing tests were pulling in opposite directions.
`TestGetNatTranslations` was right and the implementation had drifted past it
when pinhole support landed. `TestGetPortForwards::test_returns_all_rules` was
the opposite: it still expected one rule from before pinholes existed, which put
it in direct contradiction with TestIPv6Pinholes further down the same file.

tests/unit/test_driver.py

@@ -480,8 +480,15 @@ class TestGetWanStatus:
 
 
 class TestGetPortForwards:
-    def test_returns_all_rules(self, driver):
-        assert len(driver.get_port_forwards()) == 1
+    def test_returns_ipv4_mappings_and_ipv6_pinholes(self, driver):
+        """One IPv4 mapping plus one IPv6 pinhole.
+
+        This asserted 1 from before pinhole support existed, which put it in
+        direct contradiction with TestIPv6Pinholes further down the same file.
+        """
+        forwards = driver.get_port_forwards()
+        assert len(forwards) == 2
+        assert {f["protocol"] for f in forwards} == {"TCP", "TCP6"}
 
     def test_rule_fields(self, driver):
         forward = driver.get_port_forwards()[0]
@@ -497,7 +504,10 @@ class TestGetPortForwards:
 
 
 class TestGetNatTranslations:
-    def test_derived_from_enabled_port_forwards(self, driver):
+    def test_derived_from_enabled_ipv4_port_forwards(self, driver):
+        """Only the IPv4 mapping. IPv6 pinholes are firewall holes, not
+        translations, and IPv6 does not do NAT — including them paired an IPv6
+        host with the IPv4 WAN address."""
         translations = driver.get_nat_translations()
         assert len(translations) == 1
         assert translations[0]["protocol"] == "tcp"
@@ -740,6 +750,12 @@ class TestIPv6Pinholes:
         assert ssh6["internal_port"] == 22
         assert ssh6["enabled"] is True
 
+    def test_pinholes_are_not_reported_as_nat_translations(self, driver):
+        """A pinhole opens the firewall for a globally routable address; there
+        is nothing to translate."""
+        assert all(":" not in t["inside_local"].rsplit(":", 1)[0]
+                   for t in driver.get_nat_translations())
+
     def test_no_pinholes_without_ipv6_service(self, driver):
         del driver.fc.services["WANIPv6Firewall1"]
         forwards = driver.get_port_forwards()