pf: always create multihomed states as floating

When we create a new state for multihomed sctp connections (i.e.
based on INIT/INIT_ACK or ASCONF parameters) we cannot know what
interfaces we'll be seeing that traffic on. Make those states floating,
irrespective of state policy.

MFC after: 1 week
Sponsored by: Orange Business Services

(cherry picked from commit 0fe663b2a815dcb41431543940ec51408f418392)