Fixed AsyncSniffer/sniff documentation, if iface=None it will sniff only on conf.iface

Author: ronymunitz

scapy/sendrecv.py

@@ -1007,7 +1007,7 @@ class AsyncSniffer(object):
                      we have to stop the capture after this packet.
                      --Ex: stop_filter = lambda x: x.haslayer(TCP)
         iface: interface or list of interfaces (default: None for sniffing
-               on all interfaces).
+               on conf.iface).
         monitor: use monitor mode. May not be available on all OS
         started_callback: called as soon as the sniffer starts sniffing
                           (default: None).