Added full ipv6 support (now ipv6 works both inside and outside vpn)

Added support for fine-grained fec parameter, for example -f 1:3,2:4,10:6,20:10, check UDPspeeder wiki for details.

Changed option --disable-mssfix to --mssfix <number>, --mssfix 0 is equal to the old --disable-mssfix

New option --persis-tun to create persistent tun devices without the help of additional programs.