title: ipsec.py CANT FIND THE attribute IPPROTO_ESP and socket.IPPROTO_AH
body: <p>I install the module scapy for python 2.6 and when I import this module I get this warning:</p>
  
  <blockquote>
    <p>WARNING: can't import layer ipsec: 'module' object has no attribute 'IPPROTO_AH'</p>
  </blockquote>
  
  <p>I looked in the socket attributes and i didnt find the 'IPPROTO_AH' attribute 
  In addition, i tried to edit the module ipsec.py and find way to replace IPPROTO_AH with something else but then i got WARNING WITH IPPROTO_ESP ! </p>
  
  <p>I tried edit lines in ipsec.py such as:</p>
  
  <pre><code>    overload_fields = {
      IP: {'proto': IPTest},
      IPv6: {'nh': IPTest},
      IPv6ExtHdrHopByHop: {'nh': socket.IPPROTO_AH},
      IPv6ExtHdrDestOpt: {'nh': socket.IPPROTO_AH},
      IPv6ExtHdrRouting: {'nh': socket.IPPROTO_AH},}
  
  bind_layers(IP, AH, proto=socket.IPPROTO_AH)
  bind_layers(IPv6, AH, nh=socket.IPPROTO_AH)
  </code></pre>
  
  <p>how can i fix this ? </p>