[test] Allow inbound and outbound connections supporting v2 P2P protocol

- Add an optional `supports_v2_p2p` parameter to specify if the inbound
and outbound connections support v2 P2P protocol.
- In the `addconnection_callback` which gets called when creating
outbound connections, call the `addconnection` RPC with v2 P2P protocol
support enabled.

test/functional/rpc_net.py

@@ -241,7 +241,10 @@ class NetTest(BitcoinTestFramework):
     def test_service_flags(self):
         self.log.info("Test service flags")
         self.nodes[0].add_p2p_connection(P2PInterface(), services=(1 << 4) | (1 << 63))
-        assert_equal(['UNKNOWN[2^4]', 'UNKNOWN[2^63]'], self.nodes[0].getpeerinfo()[-1]['servicesnames'])
+        if self.options.v2transport:
+            assert_equal(['UNKNOWN[2^4]', 'P2P_V2', 'UNKNOWN[2^63]'], self.nodes[0].getpeerinfo()[-1]['servicesnames'])
+        else:
+            assert_equal(['UNKNOWN[2^4]', 'UNKNOWN[2^63]'], self.nodes[0].getpeerinfo()[-1]['servicesnames'])
         self.nodes[0].disconnect_p2ps()
 
     def test_getnodeaddresses(self):