ssh/agent: fix another test to not require IPv4.

Missed a copy/paste of netPipe in change 36110.

Change-Id: I1a850dd9273d71fadc0519cf4cb2a2de6ecae4c2
Reviewed-on: https://go-review.googlesource.com/36259
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
1 file changed