[client] Report network addresses on Android for posture checks (#7235)

Android never reported its local network interfaces, so PeerNetworkRange posture checks could not be evaluated: NetworkAddresses always arrived empty.

net.Interfaces() is unusable on Android 11+ (SELinux blocks netlink), so the addresses are parsed from the interface description the host app already provides via stdnet.ExternalIFaceDiscover. The MAC filter is skipped, mirroring #5906
for iOS, since Android does not expose MACs either and nothing reads Mac server side.

client/system/network_addr_android.go

@@ -0,0 +1,89 @@
+package system
+
+import (
+	"net/netip"
+	"strings"
+)
+
+var iFaceDiscover IFaceDiscover
+
+type IFaceDiscover interface {
+	IFaces() (string, error)
+}
+
+// SetIFaceDiscover configures the Android interface discovery provider.
+func SetIFaceDiscover(discover IFaceDiscover) {
+	iFaceDiscover = discover
+}
+
+func networkAddresses() ([]NetworkAddress, error) {
+	if iFaceDiscover == nil {
+		return nil, nil
+	}
+	ifaces, err := iFaceDiscover.IFaces()
+	if err != nil {
+		return nil, err
+	}
+
+	var netAddresses []NetworkAddress
+	for _, line := range strings.Split(ifaces, "\n") {
+		addresses, ok := interfaceAddresses(line)
+		if !ok {
+			continue
+		}
+		for _, address := range addresses {
+			netAddr, ok := toNetworkAddress(address)
+			if !ok {
+				continue
+			}
+			if isDuplicated(netAddresses, netAddr) {
+				continue
+			}
+			netAddresses = append(netAddresses, netAddr)
+		}
+	}
+	return netAddresses, nil
+}
+
+func interfaceAddresses(line string) ([]string, bool) {
+	parts := strings.Split(line, "|")
+	if len(parts) != 2 {
+		return nil, false
+	}
+	flags := strings.Fields(parts[0])
+	if len(flags) != 8 {
+		return nil, false
+	}
+	up, loopback := flags[3], flags[5]
+	if up != "true" || loopback == "true" {
+		return nil, false
+	}
+	return strings.Fields(parts[1]), true
+}
+
+func toNetworkAddress(address string) (NetworkAddress, bool) {
+	prefix, err := netip.ParsePrefix(address)
+	if err != nil {
+		return NetworkAddress{}, false
+	}
+	if prefix.Addr().Is4In6() {
+		if prefix.Bits() < 96 {
+			return NetworkAddress{}, false
+		}
+		prefix = netip.PrefixFrom(prefix.Addr().Unmap(), prefix.Bits()-96)
+	}
+	ip := prefix.Addr()
+	if ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsMulticast() {
+		return NetworkAddress{}, false
+	}
+	return NetworkAddress{NetIP: prefix}, true
+}
+
+func isDuplicated(addresses []NetworkAddress, addr NetworkAddress) bool {
+	for _, duplicated := range addresses {
+		if duplicated.NetIP == addr.NetIP {
+			return true
+		}
+	}
+	return false
+}