Merge pull request #1496 in SNORT/snort3 from ~STECHEW/snort3:splitter_scan to master

Merge pull request #1496 in SNORT/snort3 from ~STECHEW/snort3:splitter_scan to master

Squashed commit of the following:

commit 891499867ff983216f15e6d96b972046aba69c92
Author: Steve Chew <stechew@cisco.com>
Date:   Wed Jan 30 21:52:24 2019 +0530

    stream: Pass Packet in flush_pdu_* -> paf_eval -> paf_callback chain.

commit f1b109aff3032302542e33b3c3c4213d254a4f9e
Author: Steve Chew <stechew@cisco.com>
Date:   Tue Jan 29 02:13:40 2019 +0530

    stream: Change StreamSplitter::scan to take a Packet instead of a Flow.