Why don't you talk with him and ask him to stop first or find a way to contain the smell. Bit extreme going for the police with no formal warning first.
Cut some onions in half and place the halves in bowls of water. Put them on the window sill with the windows open. Ive done this at work to help get rid of the strong smell of fresh paint in newly decorated houses.
Having friends/family round with the flat smelling like a drugs den is really embarrassing.
are the police even interested in Cannabis any more?
If you don't want to face him in person put a note under his door warning him that the apartment smells of ganga and if he doesn't take actions to reduce the smell then official complaints will be made to authorities.
grow a pair and tell him to get it under control (by leaning out the window or something at least) or you'll get the authorities, then if he doesn't listen, kill him and smoke all his drugs.