lif: don't fail test when at least one version of INET protocols is available

This is not perfect but is enough for during the dual IP stack era.

Change-Id: Icd318f75b3ed8c73ccd588be8122379b263651fb
Reviewed-on: https://go-review.googlesource.com/41514
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

lif/address_test.go

@@ -78,15 +78,17 @@ type addrPack struct {
 }
 
 func addrPacks() ([]addrPack, error) {
+	var lastErr error
 	var aps []addrPack
 	for _, af := range [...]int{sysAF_UNSPEC, sysAF_INET, sysAF_INET6} {
 		as, err := Addrs(af, "")
 		if err != nil {
-			return nil, err
+			lastErr = err
+			continue
 		}
 		aps = append(aps, addrPack{af: af, as: as})
 	}
-	return aps, nil
+	return aps, lastErr
 }
 
 func TestAddrs(t *testing.T) {

lif/link_test.go

@@ -21,15 +21,17 @@ type linkPack struct {
 }
 
 func linkPacks() ([]linkPack, error) {
+	var lastErr error
 	var lps []linkPack
 	for _, af := range [...]int{sysAF_UNSPEC, sysAF_INET, sysAF_INET6} {
 		lls, err := Links(af, "")
 		if err != nil {
-			return nil, err
+			lastErr = err
+			continue
 		}
 		lps = append(lps, linkPack{af: af, lls: lls})
 	}
-	return lps, nil
+	return lps, lastErr
 }
 
 func TestLinks(t *testing.T) {