pf: support SCTP multihoming

SCTP may announce additional IP addresses it'll use in the INIT/INIT_ACK
chunks, or in ASCONF chunks at any time during the connection. Parse these
parameters, evaluate the ruleset for the new connection and if allowed
create the corresponding states.

MFC after: 3 weeks
Sponsored by: Orange Business Services
Differential Revision: https://reviews.freebsd.org/D41637