This patch fixes two bugs related to the setting of the I-Bit
for SCTP DATA and I-DATA chunks.

• For fragmented user messages, set the I-Bit only on the last fragment.
• When using explicit EOR mode, set the I-Bit on the last fragment, whenever SCTP_SACK_IMMEDIATELY was set in snd_flags for any of the send() calls.

Approved by: re (hrs)
MFC after: 1 week