[dsmesock] Fix io watch resource leaks. JB#37757
[dsmesock] Fix io watch resource leaks. JB#37757

Holding io channel references and leaking source ids makes dsmesock logic
unable to release all resources on exit / client disconnect.

Refactor the code so that source ids are held instead of channel refs.

Signed-off-by: Simo Piiroinen <6d5e5360bed3d486f7d9fb26b0f737f7d4fd45ee@jollamobile.com>

spiiroin/dsme,spiiroin/dsme