osmux: Keep decoding osmux pkt if a batch contains an unknown CID

Receiving an unknown CID (for which we don't have an active conn) is
totally expected at the end of the call, were some messages from the
peer may be send for a while, specially if latency is high.
If this occurs, we simply drop that batch and keep decoding the osmux
message in order to keep delivering content to other circuits.

Related: SYS#5987
Change-Id: I315949853bdcc07bef15d2e8579029cc72c427cf
1 file changed