Fix compiler warning: defined but not used

../Sources/yapi/ytcp.c:118: warning: ‘yNetLogErrEx’ defined but not used

This is because yNetLogErr() (or yNetLogErrEx()) is used only in code
compiled when Y_UPNP_DETECT is defined.

Y_UPNP_DETECT is _not_ defined by default so the compiler generates the
warning