MFC r351638: Improve handling DATA chunks.

Improve the handling of illegal sequence number combinations in received
data chunks. Abort the association if there are data chunks with larger
fragement sequence numbers than the fragement sequence of the last
fragment.
Thanks to Mark Wodrich from Google who found this issue by fuzz testing
the userland stack and reporting this issue in
https://github.com/sctplab/usrsctp/issues/355