Improve random number generation on Linux and Windows.
Improve random number generation on Linux and Windows.

Thanks to Felix Wilhelm for suggesting the improvement.

sctplab/usrsctp,weinrank/usrsctp,sctplab/usrsctp,CoolmanCZ/usrsctp,CoolmanCZ/usrsctp,sctplab/usrsctp,CoolmanCZ/usrsctp,CoolmanCZ/usrsctp,weinrank/usrsctp,weinrank/usrsctp