--bt-detach-seed-only[=true|false]
Exclude seed only downloads when counting
concurrent active downloads (See -j option).
This means that if -j3 is given and this option
is turned on and 3 downloads are active and one
of those enters seed mode, then it is excluded
from active download count (thus it becomes 2),
and the next download waiting in queue gets
started. But be aware that seeding item is still
recognized as active download in RPC method.