修复启用KCP情况下可能存在服务器无法正常给客户端发送消息问题

[lfeng1420]

类似#523。当服务器收到另一个客户端的消息时，由于已经覆盖了io的peeraddr，服务器无法再给覆盖前的客户端发送消息。
本地改动了下evpp目录下的UdpServer_test.cpp和UdpClient_test.cpp进行了验证，可以正常通信。

/*
 * UdpServer_test.cpp
 *
 * @build   make evpp
 * @server  bin/UdpServer_test 1234
 * @client  bin/UdpClient_test 1234
 *
 */

#include <iostream>
#include <map>
#include <string>
#include "hstring.h"

#include "UdpServer.h"

using namespace hv;

int main(int argc, char* argv[]) {
    if (argc < 2) {
        printf("Usage: %s port\n", argv[0]);
        return -10;
    }
    int port = atoi(argv[1]);

    std::map<std::string, sockaddr_u> addrMap;
    UdpServer srv;
    kcp_setting_t stSetting;
    kcp_setting_init_with_normal_mode(&stSetting);
    srv.setKcp(&stSetting);
    int bindfd = srv.createsocket(port);
    if (bindfd < 0) {
        return -20;
    }
    printf("server bind on port %d, bindfd=%d ...\n", port, bindfd);
    srv.onMessage = [&](const SocketChannelPtr& channel, Buffer* buf) {
        std::string addr = channel->peeraddr();
        addrMap[addr] = *(sockaddr_u*)hio_peeraddr(channel->io());

        // echo
        printf("< %s %.*s\n", addr.c_str(), (int)buf->size(), (char*)buf->data());
        channel->write(buf);
    };
    srv.start();

    std::string str;
    while (std::getline(std::cin, str)) {
        if (str == "close") {
            srv.closesocket();
        } else if (str == "start") {
            srv.start();
        } else if (str == "stop") {
            srv.stop();
            break;
        } else {
            hv::StringList stringList = split(str, ' ');
            if (stringList.size() == 2) {
                auto addrIt = addrMap.find(stringList[0]);
                if (addrIt != addrMap.end()) {
                    printf("> send %s to %s\n", stringList[1].c_str(), stringList[0].c_str());
                    srv.sendto(stringList[1], (sockaddr*)&addrIt->second);
                }
            }
            else {
                srv.sendto(str);
            }
        }
    }

    return 0;
}

/*
 * UdpClient_test.cpp
 *
 * @build   make evpp
 * @server  bin/UdpServer_test 1234
 * @client  bin/UdpClient_test 1234
 *
 */

#include <iostream>

#include "UdpClient.h"
#include "htime.h"

using namespace hv;

int main(int argc, char* argv[]) {
    if (argc < 2) {
        printf("Usage: %s remote_port [remote_host]\n", argv[0]);
        return -10;
    }
    int remote_port = atoi(argv[1]);
    const char* remote_host = "127.0.0.1";
    if (argc > 2) {
        remote_host = argv[2];
    }

    UdpClient cli;
    kcp_setting_t stSetting;
    kcp_setting_init_with_normal_mode(&stSetting);
    cli.setKcp(&stSetting);
    int sockfd = cli.createsocket(remote_port, remote_host);
    if (sockfd < 0) {
        return -20;
    }
    printf("client sendto port %d, sockfd=%d ...\n", remote_port, sockfd);
    cli.onMessage = [](const SocketChannelPtr& channel, Buffer* buf) {
        printf("< %.*s\n", (int)buf->size(), (char*)buf->data());
    };
    cli.start();

    std::string str;
    while (std::getline(std::cin, str)) {
        if (str == "close") {
            cli.closesocket();
        } else if (str == "start") {
            cli.start();
        } else if (str == "stop") {
            cli.stop();
            break;
        } else {
            cli.sendto(str);
        }
    }

    return 0;
}