Fix buffering packets in LINC when packet_in is sent (OFP 1.3)

There has been an incorrect assumption that buffered packets are
wrapped into a #linc_pkt. This resulted in a crash while matching
on the packet.

(Motivated by #322).
Fix buffering packets in LINC when packet_in is sent (OFP 1.4)

There has been an incorrect assumption that buffered packets are
wrapped into a #linc_pkt. This resulted in a crash while matching
on the packet.

(Motivated by #322).
Merge pull request #324 from FlowForwarding/buffer_packets_crash

Fix buffering packets when packet in is sent