fix signed/unsigned in strprintf and CNetAddr::GetByte()

- I checked every occurance of strprintf() in the code and used %u, where
  unsigned vars are used
- the change to GetByte() was made, as ip is an unsigned char

src/net.cpp

@@ -1025,7 +1025,7 @@ void ThreadMapPort2(void* parg)
 {
     printf("ThreadMapPort started\n");
 
-    std::string port = strprintf("%d", GetListenPort());
+    std::string port = strprintf("%u", GetListenPort());
     const char * multicastif = 0;
     const char * minissdpdpath = 0;
     struct UPNPDev * devlist = 0;