Replace ChanType.sepfds with Channel.bidir_fd This handles the case where a svrchansess has separate FDs for nopty, but a single FD for pty mode. The use of sepfds was also previously incorrect for X11 and agent forwarding

#include "fuzz.h"

int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
	return fuzz_run_client(Data, Size, 1);
}