replace SSRC source from IPv4 address to random number

Previous implementation uses SSRC as IPv4 address that is same behaviour
of Kenwood's NXDN repeater.

RFC 3350 RTP protocol recommends SSRC uses random number.
So I use MT19937 random number generator instead of IP address.

And if this is no problem, I will do two changes.

- replace rand() in DMRNetwork.cpp and DStarNetwork.cpp to MT19937
- remove getLocalAddress() in UDPSocket.cpp

NXDNKenwoodNetwork.cpp

@@ -56,7 +56,8 @@ m_rtcpTimer(1000U, 0U, 200U),
 m_hangTimer(1000U, 5U),
 m_hangType(0U),
 m_hangSrc(0U),
-m_hangDst(0U)
+m_hangDst(0U),
+m_random()
 {
 	assert(localPort > 0U);
 	assert(!gwyAddress.empty());
@@ -65,6 +66,10 @@ m_hangDst(0U)
 	m_sacch = new unsigned char[10U];
 
 	m_address = CUDPSocket::lookup(gwyAddress);
+
+	std::random_device rd;
+	std::mt19937 mt(rd());
+	m_random = mt;
 }
 
 CNXDNKenwoodNetwork::~CNXDNKenwoodNetwork()
@@ -87,7 +92,7 @@ bool CNXDNKenwoodNetwork::open()
 		return false;
 	}
 
-	m_ssrc = m_rtpSocket.getLocalAddress();
+	m_ssrc = m_random();
 
 	return true;
 }

NXDNKenwoodNetwork.h

@@ -25,6 +25,7 @@
 
 #include <cstdint>
 #include <string>
+#include <random>
 
 class CNXDNKenwoodNetwork : public INXDNNetwork {
 public:
@@ -69,6 +70,7 @@ private:
     unsigned char  m_hangType;
     unsigned short m_hangSrc;
     unsigned short m_hangDst;
+    std::mt19937   m_random;
 
     bool processIcomVoiceHeader(const unsigned char* data);
     bool processIcomVoiceData(const unsigned char* data);