stream: improve retransmission handling

When connection are closing, don't reject retransmissions of data
packets.

Bug #1180. https://redmine.openinfosecfoundation.org/issues/1180

Prscript:
- PR build: https://buildbot.suricata-ids.org/builders/inliniac/builds/265
- PR pcaps: https://buildbot.suricata-ids.org/builders/inliniac-pcap/builds/184