nettest: re-enable unixpacket tests on netbsd/386

The tests seem to work fine on netbsd/386 (NetBSD 9.3). This reverts CL
80755.

Updates golang/go#22927

Change-Id: I480ac82b10e85aa0fc081e76fbbcbc75f3ee7d38
Reviewed-on: https://go-review.googlesource.com/c/net/+/483375
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

nettest/nettest.go

@@ -126,12 +126,6 @@ func TestableNetwork(network string) bool {
 		switch runtime.GOOS {
 		case "aix", "android", "fuchsia", "hurd", "darwin", "ios", "js", "nacl", "plan9", "windows", "zos":
 			return false
-		case "netbsd":
-			// It passes on amd64 at least. 386 fails
-			// (Issue 22927). arm is unknown.
-			if runtime.GOARCH == "386" {
-				return false
-			}
 		}
 	}
 	switch ss[0] {