Replace unix.SYS_IOCTL with unix.Ioctl{Get,Set}Termios

[priyawadhwa]

I'm trying to import OpenTelemetry into my project, but Darwin builds are failing with this error:

# github.com/moby/hyperkit/go
../go/pkg/mod/github.com/moby/hyperkit@v0.0.0-20171020124204-a12cd7250bcd/go/pty_util_darwin.go:24:31: undefined: unix.SYS_IOCTL

The bug seems to be here:

hyperkit/go/pty_util_darwin.go

Line 24 in b54460a

if _, _, err := unix.Syscall(unix.SYS_IOCTL, fd, flag, data); err != 0 {

Go recently updated the sys package to remove direct system calls on Darwin (ory/dockertest#212 (comment))

Other moby projects have merged PRs to update the system call (moby/term#16).

Would it be possible to update this syscall? I'm happy to open a PR if that helps.