Fix masking of irrelevant bits in address groups.

src/netbase.cpp

@@ -983,7 +983,7 @@ std::vector<unsigned char> CNetAddr::GetGroup() const
         nBits -= 8;
     }
     if (nBits > 0)
-        vchRet.push_back(GetByte(15 - nStartByte) | ((1 << nBits) - 1));
+        vchRet.push_back(GetByte(15 - nStartByte) | ((1 << (8 - nBits)) - 1));
 
     return vchRet;
 }