net: relax TestInterfaces and TestInterfaceAddrs for BSD variants

Fixes #15249.

Change-Id: I91fc3d6a2df294b21a67d085da6fe661827a850e
Reviewed-on: https://go-review.googlesource.com/22079Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/interface_test.go

@@ -183,10 +183,16 @@ func testInterfaceMulticastAddrs(t *testing.T, ifi *Interface) (nmaf4, nmaf6 int
 }
 
 func testAddrs(t *testing.T, ifat []Addr) (naf4, naf6 int) {
+	// Note: BSD variants allow assigning any IPv4/IPv6 address
+	// prefix to IP interface. For example,
+	//   - 0.0.0.0/0 through 255.255.255.255/32
+	//   - ::/0 through ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff/128
+	// In other words, there is no tightly-coupled combination of
+	// interface address prefixes and connected routes.
 	for _, ifa := range ifat {
 		switch ifa := ifa.(type) {
 		case *IPNet:
-			if ifa == nil || ifa.IP == nil || ifa.IP.IsUnspecified() || ifa.IP.IsMulticast() || ifa.Mask == nil {
+			if ifa == nil || ifa.IP == nil || ifa.IP.IsMulticast() || ifa.Mask == nil {
 				t.Errorf("unexpected value: %#v", ifa)
 				continue
 			}
@@ -219,7 +225,7 @@ func testAddrs(t *testing.T, ifat []Addr) (naf4, naf6 int) {
 			}
 			t.Logf("interface address %q", ifa.String())
 		case *IPAddr:
-			if ifa == nil || ifa.IP == nil || ifa.IP.IsUnspecified() || ifa.IP.IsMulticast() {
+			if ifa == nil || ifa.IP == nil || ifa.IP.IsMulticast() {
 				t.Errorf("unexpected value: %#v", ifa)
 				continue
 			}