MEDIUM: fd: make fd_insert() take local thread masks

MEDIUM: fd: make fd_insert() take local thread masks

fd_insert() was already given a thread group ID and a global thread mask.
Now we're changing the few callers to take the group-local thread mask
instead. It's passed directly into the FD's thread mask. Just like for
previous commit, it must not change anything when a single group is
configured.