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/netbase.h

@@ -66,7 +66,7 @@ class CNetAddr
         enum Network GetNetwork() const;
         std::string ToString() const;
         std::string ToStringIP() const;
-        int GetByte(int n) const;
+        unsigned int GetByte(int n) const;
         uint64 GetHash() const;
         bool GetInAddr(struct in_addr* pipv4Addr) const;
         std::vector<unsigned char> GetGroup() const;