net: re-enable unixpacket tests on netbsd/386

net: re-enable unixpacket tests on netbsd/386

The tests seem to work fine on netbsd/386 (NetBSD 9.3). This reverts CL
80756.

Updates #22927

Change-Id: I2235d69129aa81b43513a171834d058f47cd9933
Reviewed-on: https://go-review.googlesource.com/c/go/+/483395
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>