unix: fix IoctlGetPtmget get empty ptsname on NetBSD

[iyzyi]

On NetBSD, because the size of the Ptmget structure does not match
the value of TIOCPTSNAME, IoctlGetPtmget uses an incorrect structure
internally, resulting in empty ptsname.

See https://github.com/NetBSD/src/blob/trunk/sys/sys/ttycom.h

Fixes golang/go#66871

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from iyzyi:

Patch Set 3:

(1 comment)

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