obexd: queue transfers in ftp sessions
obexd: queue transfers in ftp sessions

Previous implementation reported busy when trying to queue several
transfers in the same session.

pkarasev3/bluez,silent-snowman/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,mapfau/bluez,silent-snowman/bluez,ComputeCycles/bluez,pkarasev3/bluez,ComputeCycles/bluez,mapfau/bluez,ComputeCycles/bluez,pkarasev3/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,mapfau/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez