pf: Track the original kif for floating states

Track (and display) the interface that created a state, even if it's a
floating state (and thus uses virtual interface 'all').

MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D30245

(cherry picked from commit d0fdf2b28f9b981d2cb98e9da8a715e046ef1e92)