[test] enable NAT64 translator unit tests (#11845)

This commit makes several updates to enable and fix NAT64 unit test

- Enables the NAT64 translator in `toranj` test configs, ensuring
  that the `test_nat64` unit test is now covered by the GitHub
  Actions CI (under the `toranj` workflow).
- Enable `OPENTHREAD_CONFIG_NAT64_PORT_TRANSLATION_ENABLE` for the POSIX
  `toranj` build while disabling it for the simulation build, ensuring
  both configurations are built and covered by CI.
- Fixes the `test_nat64` unit test by removing an incorrect
  "mapping pool exhausted" step. This step is now invalid as the pool
  size is configured to a much larger value (254) via
  `OPENTHREAD_CONFIG_NAT64_MAX_MAPPINGS`.

src/posix/platform/netif.cpp

@@ -161,9 +161,6 @@ extern int
 
 unsigned int gNetifIndex = 0;
 char         gNetifName[IFNAMSIZ];
-#if OPENTHREAD_CONFIG_NAT64_TRANSLATOR_ENABLE
-static otIp4Cidr sActiveNat64Cidr;
-#endif
 
 const char *otSysGetThreadNetifName(void) { return gNetifName; }
 
@@ -214,10 +211,6 @@ static uint8_t            sAddedExternalRoutesNum = 0;
 static otIp6Prefix        sAddedExternalRoutes[kMaxExternalRoutesNum];
 #endif
 
-#if OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE && OPENTHREAD_CONFIG_NAT64_TRANSLATOR_ENABLE
-static constexpr uint32_t kNat64RoutePriority = 100; ///< Priority for route to NAT64 CIDR, 100 means a high priority.
-#endif
-
 #if defined(RTM_NEWMADDR) || defined(__NetBSD__)
 // on some BSDs (mac OS, FreeBSD), we get RTM_NEWMADDR/RTM_DELMADDR messages, so we don't need to monitor using MLD
 // on NetBSD, MLD monitoring simply doesn't work
@@ -976,6 +969,11 @@ static void processAddressChange(const otIp6AddressInfo *aAddressInfo, bool aIsA
 }
 
 #if defined(__linux__) && OPENTHREAD_CONFIG_NAT64_TRANSLATOR_ENABLE
+
+static otIp4Cidr sActiveNat64Cidr;
+
+static constexpr uint32_t kNat64RoutePriority = 100; // Priority for route to NAT64 CIDR, 100 means a high priority.
+
 static bool isSameIp4Cidr(const otIp4Cidr &aCidr1, const otIp4Cidr &aCidr2)
 {
     bool res = true;

tests/toranj/openthread-core-toranj-config-posix.h

@@ -70,6 +70,8 @@
 
 #define OPENTHREAD_POSIX_CONFIG_NAT64_AIL_PREFIX_ENABLE 1
 
+#define OPENTHREAD_CONFIG_NAT64_PORT_TRANSLATION_ENABLE 1
+
 // The following two features (`USE_HEAP`) are set explicitly on posix `toranj`
 // to validate the build with these config. The `toranj` build under simulation
 // platform covers the opposite configs (allows `USE_HEAP`).

tests/toranj/openthread-core-toranj-config-simulation.h

@@ -93,6 +93,8 @@
 
 #define OPENTHREAD_CONFIG_DHCP6_CLIENT_ENABLE 1
 
+#define OPENTHREAD_CONFIG_NAT64_PORT_TRANSLATION_ENABLE 0
+
 #define OPENTHREAD_CONFIG_RADIO_STATS_ENABLE 0
 
 #define OPENTHREAD_CONFIG_TREL_MANAGE_DNSSD_ENABLE 0

tests/toranj/openthread-core-toranj-config.h

@@ -54,6 +54,8 @@
 
 #define OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
 
+#define OPENTHREAD_CONFIG_NAT64_TRANSLATOR_ENABLE OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
+
 #define OPENTHREAD_CONFIG_BORDER_ROUTING_DHCP6_PD_ENABLE 1
 
 #define OPENTHREAD_CONFIG_BORDER_ROUTING_DHCP6_PD_CLIENT_ENABLE 1

tests/unit/test_nat64.cpp

@@ -314,17 +314,6 @@ void TestNat64(void)
         TestCase4To6("no v4 mapping", kIp4Packet, Nat64::Translator::kDrop, nullptr, 0);
     }
 
-    {
-        // fd02::2               fd01::ac10:f3c5       UDP      52     43981 → 4660 Len=4
-        const uint8_t kIp6Packet[] = {
-            0x60, 0x08, 0x6e, 0x38, 0x00, 0x0c, 0x11, 0x40, 0xfd, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-            0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xfd, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-            172,  16,   243,  197,  0xab, 0xcd, 0x12, 0x34, 0x00, 0x0c, 0xe3, 0x30, 0x61, 0x62, 0x63, 0x64,
-        };
-
-        TestCase6To4("mapping pool exhausted", kIp6Packet, Nat64::Translator::kDrop, nullptr, 0);
-    }
-
     testFreeInstance(sInstance);
 }