sctp: improve handling of stale cookie error causes

• If a measure of staleness of 0 is reported, use the RTT instead.
• Ensure that we always send a cookie preservative parameter by rounding up during the calculation.
• If allowed, perform a round trip time measurement.
• Clear the overall error counter, since the error cause also acts like an ACK.

(cherry picked from commit 1f0e13449beef3a983d9ed2faf4734075e4120d1)