Comment 1 for bug 1426667

I've done a little bit more investigating and It looks like the -1 check actually is getting performed. The cause of the bug is actually more simple: recvfrom returns a (32-bit) signed int, but the recvfrom ffi definition has a return type of ssize_t, I assume that's a 64bit int on x86_64 systems. This would cause the -1 error status to get marshalled into Lisp incorrectly.