filemon: Reject FILEMON_SET_FD commands when the fd is a kqueue

When FILEMON_SET_FD is used, the filemon handle effectively wraps the
passed file. In particular, the handle may be inherited by a child
process, or transferred over a unix domain socket, so we must verify
that the backing file permits this.

Reported by: syzbot+36e6be9e02735fe66ca8@syzkaller.appspotmail.com
Reviewed by: emaste
Sponsored by: The FreeBSD Foundation

(cherry picked from commit b84ed4e7f626de5475cf26bae6d7ff15ec9f9675)