Merge pull request #992 from buger/fix/989-duplicate

Issue was introduced while fixing windows c9274ac

Added exception for Windows, which by default allows interfaces without IPs.
Interface name check moved higher, so if interface namee or IP match, rest of check will be ignored.

Additionally windows npcap loopback mechanism can now be picked by specifying 127.0.0.1 or loopback IP.

Fix #989

capture/capture.go

@@ -598,12 +598,27 @@ func (l *Listener) setInterfaces() (err error) {
 			return
 		}
 
+		if runtime.GOOS != "windows" {
+			if len(pi.Addresses) == 0 {
+				continue
+			}
+
+			if ni.Flags&net.FlagUp == 0 {
+				continue
+			}
+		}
+
 		l.Interfaces = append(l.Interfaces, pi)
 	}
 	return
 }
 
 func isDevice(addr string, ifi pcap.Interface) bool {
+	// Windows npcap loopback have no IPs
+	if addr == "127.0.0.1" && ifi.Name == `\Device\NPF_Loopback` {
+		return true
+	}
+
 	if addr == ifi.Name {
 		return true
 	}