rtp send rtp g711 audio can config duration (#3325)

optimization for this
[issue](https://github.com/ZLMediaKit/ZLMediaKit/issues/3316)

src/Common/config.cpp

@@ -338,6 +338,7 @@ const string kH265PT = RTP_PROXY_FIELD "h265_pt";
 const string kPSPT = RTP_PROXY_FIELD "ps_pt";
 const string kOpusPT = RTP_PROXY_FIELD "opus_pt";
 const string kGopCache = RTP_PROXY_FIELD "gop_cache";
+const string kRtpG711DurMs = RTP_PROXY_FIELD "rtp_g711_dur_ms";
 
 static onceToken token([]() {
     mINI::Instance()[kDumpDir] = "";
@@ -348,6 +349,7 @@ static onceToken token([]() {
     mINI::Instance()[kPSPT] = 96;
     mINI::Instance()[kOpusPT] = 100;
     mINI::Instance()[kGopCache] = 1;
+    mINI::Instance()[kRtpG711DurMs] = 100;
 });
 } // namespace RtpProxy
 

src/Common/config.h

@@ -382,6 +382,9 @@ extern const std::string kPSPT;
 extern const std::string kOpusPT;
 // RtpSender相关功能是否提前开启gop缓存优化级联秒开体验，默认开启
 extern const std::string kGopCache;
+//国标发送g711 rtp 打包时，每个包的语音时长是多少，默认是100 ms，范围为20~180ms (gb28181-2016，c.2.4规定)，
+//最好为20 的倍数，程序自动向20的倍数取整
+extern const std::string kRtpG711DurMs;
 } // namespace RtpProxy
 
 /**