rrdstats:
 * ensure wget-gnu is used if FREETZ_PACKAGE_RRDSTATS_CABLEMODEM_WGET is selected and wget-gnu is external'ed
 * fixes #2364


git-svn-id: file:///var/svn/freetz/trunk@11683 149334a1-2f27-0410-a3b9-fc62619ac1e6