[mncc] Fix possible transaction/subscriber and real life subscriber leak

In the case a transaction has been already scheduled return 0 was
called but the subscriber and transaction would leak. Fix it by
calling subscr_put and trans_free.

After claiming the channel also remove the reference on the subscr.
1 file changed
tree: af2e5e800dd24e2b5f42a1f670d2fb1daaf9dadd
  1. hlrsync/
  2. linux-kernel/
  3. openbsc/
  4. wireshark/