DHT node RTT fix

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code/branches/RC_1_0@10450 a83610d8-ad2a-0410-a6ab-fc0612d85776
fix bug in DHT routing table node-id prefix optimization

git-svn-id: svn://svn.code.sf.net/p/libtorrent/code/branches/RC_1_0@10451 a83610d8-ad2a-0410-a6ab-fc0612d85776