The arm5 and mips builders are can't-send-a-packet-to-localhost-in-1s
slow apparently. 1m is less useful, but still better than an obscure
test timeout panic.

Fixes #28405

Change-Id: I2feeae6ea1b095114caccaab4f6709f405faebad
Reviewed-on: https://go-review.googlesource.com/c/145037
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>