Multi-link PPP protocol daemon MPD5 remotely exploitable crash

Version 5.9 contains security fix for L2TP clients and servers.
Insufficient validation of incoming L2TP control packet
specially crafted by unauthenticated user might lead to unexpected
termination of the process. The problem affects mpd versions
since 4.0 that brought in initial support for L2TP.
Installations not using L2TP clients nor L2TP server configuration were not affected.