使用NEVPNProtocolIKEv2来开发VPN，iOS 14之前正常使用，iOS 14发现 startVPNTunnelAndReturnError 没有报错，但是VPN的状态是NEVPNStatusDisconnecting
通过运行iOS13和iOS14打印比较，发现有些参数的默认值发生改变
NEVPNProtocolIKEv2 *protocol = [[NEVPNProtocolIKEv2 alloc] init];
NSLog(@"------%ld",(long)protocol.IKESecurityAssociationParameters.diffieHellmanGroup);
NSLog(@"------%ld",(long)protocol.IKESecurityAssociationParameters.encryptionAlgorithm);
NSLog(@"------%ld",(long)protocol.IKESecurityAssociationParameters.integrityAlgorithm);
NSLog(@"------%ld",(long)protocol.IKESecurityAssociationParameters.lifetimeMinutes);
