Only set the ipfilter running state to 'not running' if we are
doing the teardown. ipf_destroy_all() may free ipfmain in case
of ipf_dynamic_softc being true, thus we are avoiding a possible
memory modified after free as well.

Reported by: Coverity
Coverity CID: 1357320
Approved by: re (hrs)
MFC after: 10 days