Traversal: Use a decent PRNG instead of rand()

we don’t need cryptosecure random, but having a uniform distribution is
always better.

Source/Core/Common/TraversalClient.cpp

@@ -7,9 +7,10 @@ static void GetRandomishBytes(u8* buf, size_t size)
 {
 	// We don't need high quality random numbers (which might not be available),
 	// just non-repeating numbers!
-	srand(enet_time_get());
+	static std::mt19937 prng(enet_time_get());
+	static std::uniform_int_distribution<unsigned int> u8_distribution(0, 255);
 	for (size_t i = 0; i < size; i++)
-		buf[i] = rand() & 0xff;
+		buf[i] = u8_distribution(prng);
 }
 
 TraversalClient::TraversalClient(ENetHost* netHost, const std::string& server, const u16 port)

Source/Core/Common/TraversalClient.h

@@ -4,6 +4,7 @@
 #include <functional>
 #include <list>
 #include <memory>
+#include <random>
 #include <enet/enet.h>
 #include "Common/Common.h"
 #include "Common/Thread.h"