Improve the initialization of the random number generator on platforms not providing arc4random_buf().
Improve the initialization of the random number generator
on platforms not providing arc4random_buf().

Thanks to Natalie Silvanovich of Google Project Zero for
finding and reporting the issue.

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