dns/cascade: Fix store global state

Cascade fails to create its global state file and therefore loses any
configured zones on a restart. Upstream may have included a compiled-in
default value of /var/lib/cascade/state.db, but this path does not exist
under FreeBSD and the directory is not being created by pkg. Specifying
a valid filename using the --state option when starting cascaded appears
to rectify the issue.

PR: 292208
Reported by: colin@fbg22.ksac.uk