net: disable "tcp" test on openbsd

Doing a socket/listen on an unspecified address with an unspecified
address family is likely to result in an AF_INET6 socket on an IPv6
capable system, which under OpenBSD means IPv6 only - not IPv4 *and*
IPv6. In this case trying to connect to this socket from an IPv4
loopback address is not going to end well.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4807057

src/pkg/net/server_test.go

@@ -115,7 +115,9 @@ func doTest(t *testing.T, network, listenaddr, dialaddr string) {
 }
 
 func TestTCPServer(t *testing.T) {
-	doTest(t, "tcp", "", "127.0.0.1")
+	if syscall.OS != "openbsd" {
+		doTest(t, "tcp", "", "127.0.0.1")
+	}
 	doTest(t, "tcp", "0.0.0.0", "127.0.0.1")
 	doTest(t, "tcp", "127.0.0.1", "127.0.0.1")
 	doTest(t, "tcp4", "", "127.0.0.1")

src/pkg/net/tcpsock_posix.go

@@ -12,6 +12,11 @@ import (
 	"syscall"
 )
 
+// BUG(rsc): On OpenBSD, listening on the "tcp" network does not listen for
+// both IPv4 and IPv6 connections. This is due to the fact that IPv4 traffic
+// will not be routed to an IPv6 socket - two separate sockets are required
+// if both AFs are to be supported. See inet6(4) on OpenBSD for details.
+
 func sockaddrToTCP(sa syscall.Sockaddr) Addr {
 	switch sa := sa.(type) {
 	case *syscall.SockaddrInet4: