Add IoctlGetInt/IoctlSetInt, IoctlGetTermios/IoctlSetTermios and
IoctlGetWinsize/IoctlSetWinsize on NetBSD. These are similar to the
already existing implementations on Linux, Darwin and Solaris.

Change-Id: I6c38d946b9f461c8e4c6c5e044aaff9b37e4b02f
Reviewed-on: https://go-review.googlesource.com/76171Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>