Merge branch 'sctp-transmit-errs'

Xin Long says:

====================
sctp: fix the transmit err process

This patchset is to improve the transmit err process and also fix some
issues.

After this patchset, once the chunks are enqueued successfully, even
if the chunks fail to send out, no matter because of nodst or nomem,
no err retruns back to users any more. Instead, they are taken care
of by retransmit.

v1->v2:
  - add more details to the changelog in patch 1/6
  - add Fixes: tag in patch 2/6, 3/6
  - also revert 69b5777f2e57 in patch 3/6
====================

Signed-off-by: David S. Miller <davem@davemloft.net>