title: Why uses scapy wrong source mac-adress with 'sendp()'
body: <p>I use the function <code>sendp()</code> in scapy to send some messages at layer2.
  My pc has 6 LAN interfaces and I specify one interface (enp2s0f0) in <code>sendp()</code>.</p>
  
  <p>When I observe the sent packets with wireshark, I can see that the source address is not from my specified interface. Instead it is from another interface of the pc.</p>
  
  <pre><code> packet = Ether(dst='ff:ff:ff:ff:ff:ff' ,  type = 0x8011 )
   packet = packet / msg
   sendp(packet, iface='enp2s0f0')
  </code></pre>
  
  <p>The MAC-address from enp2s0f0 is <code>\**:\**:\**:4b:3c:00</code>. 
  Wireshark shows the source address from the sent packet <code>\*\*:\**:\**:4b:3c:01</code>.
  This is also a valid mac-address from an interface of my pc, but at this port is nothing connected.</p>
  
  <p>How can I force scapy, to use the correct source-address?</p>