[tests] add tests for NAT64 prefix advertisement (#7361)

This commit adds tests for NAT64 prefix
advertisement. BORDER_ROUTING_NAT64 is set to 1 to enable the feature
in tests.

It also adjusted some util functions for prefixes and routes in
netdata.

Testing outbound connectivity to IPv4 hosts is not covered yet. It
will be added after we update OTBR.

tests/scripts/thread-cert/node.py

@@ -1897,16 +1897,41 @@ class NodeImpl:
         self.send_command('br disable')
         self._expect_done()
 
-    def get_omr_prefix(self):
+    def get_br_omr_prefix(self):
         cmd = 'br omrprefix'
         self.send_command(cmd)
         return self._expect_command_output()[0]
 
-    def get_on_link_prefix(self):
+    def get_netdata_omr_prefixes(self):
+        prefixes = [prefix.split(' ')[0] for prefix in self.get_prefixes()]
+        return prefixes
+
+    def get_br_on_link_prefix(self):
         cmd = 'br onlinkprefix'
         self.send_command(cmd)
         return self._expect_command_output()[0]
 
+    def get_netdata_non_nat64_prefixes(self):
+        prefixes = []
+        routes = self.get_routes()
+        for route in routes:
+            if 'n' not in route.split(' ')[1]:
+                prefixes.append(route.split(' ')[0])
+        return prefixes
+
+    def get_br_nat64_prefix(self):
+        cmd = 'br nat64prefix'
+        self.send_command(cmd)
+        return self._expect_command_output()[0]
+
+    def get_netdata_nat64_prefix(self):
+        prefixes = []
+        routes = self.get_routes()
+        for route in routes:
+            if 'n' in route.split(' ')[1]:
+                prefixes.append(route.split(' ')[0])
+        return prefixes
+
     def get_prefixes(self):
         return self.get_netdata()['Prefixes']
 
@@ -1944,10 +1969,12 @@ class NodeImpl:
 
         return netdata
 
-    def add_route(self, prefix, stable=False, prf='med'):
+    def add_route(self, prefix, stable=False, nat64=False, prf='med'):
         cmd = 'route add %s ' % prefix
         if stable:
             cmd += 's'
+        if nat64:
+            cmd += 'n'
         cmd += ' %s' % prf
         self.send_command(cmd)
         self._expect_done()