I-FORWARD-TSN-Chunk is accepted when no I-DATA-Support is announced at handshake

[TheAomx]

When an INIT-Chunk like

INIT[flgs=0, tag=1, a_rwnd=1500, os=1, is=1, tsn=0, FORWARD_TSN_SUPPORTED[], SUPPORTED_EXTENSIONS[types=[FORWARD_TSN, I_FORWARD_TSN]]]

in injected and later after the handshake is completed the following I-FORWARD-TSN-Chunk is injected:

I_FORWARD_TSN[cum_tsn=1, ids=[]]

the FreeBSD-Implementation sends an SACK-Chunk instead of an ERROR-Chunk.

In section 2.3.1. of the internet draft "Stream Schedulers and User Message Interleaving for the Stream Control Transmission Protocol" it says:

Support for the I-FORWARD-TSN chunk is negotiated during the SCTP
association setup via the Supported Extensions Parameter as defined
in [RFC5061]. Only if both end points support the I-DATA chunk and
the I-FORWARD-TSN chunk, the partial reliability extension can be
used in combination with user message interleaving.

See the following test-case for more details:

• https://github.com/nplab/PR_SCTP_Testsuite/blob/master/i-forward-tsn/handshake-with-i-forward-tsn/handshake-with-i-forward-tsn-5.pkt