pf: add extra SCTP multihoming probe points

Add probe points in the SCTP multihome parsing code. This is intended to help
debug a multihome issue, and is expected to be generally useful, so will be
included for everyone.

MFC after: 2 weeks
Sponsored by: Orange Business Services

(cherry picked from commit 2d2481c35f5a53322e982e47a2bb8f9085f525b7)