Fix a bug related to fast retransmissions.
When processing a SACK advancing the cumtsn-ack in fast recovery,
increment the miss-indications for all TSN's reported as missing.
Thanks to Fabian Ising for finding the bug and to Timo Voelker
for provinding a fix.
This fix moves also CMT related initialisation of some variables
to a more appropriate place.
MFC after: 1 week