Merge branch 'sctp-refactor-sctp_outq_flush'

Marcelo Ricardo Leitner says:

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sctp: refactor sctp_outq_flush

Currently sctp_outq_flush does many different things and arguably
unrelated, such as doing transport selection and outq dequeueing.

This patchset refactors it into smaller and more dedicated functions.
The end behavior should be the same.

The next patchset will rework the function parameters.

Changes since v1:
- fix build issues on patches 3 and 4, and updated 5 and 8 because of
  it.

Changes since v2:
- fixed panic if building with just up to patch 3 applied
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Signed-off-by: NDavid S. Miller <davem@davemloft.net>