stream: special handling for RST data

stream: special handling for RST data

Data on RST packets is not invalid, but also shouldn't be used
in reassembly.

RFC 1122:

  4.2.2.12  RST Segment: RFC-793 Section 3.4

    A TCP SHOULD allow a received RST segment to include data.

    DISCUSSION
        It has been suggested that a RST segment could contain
        ASCII text that encoded and explained the cause of the
        RST.  No standard has yet been established for such
        data.

RST data will be presented to the detection engine per packet,
but will not be part of stream reassembly.

Bug: #6244.