Change from bool indicating blocked to an enum: when watches go

Change from bool indicating blocked to an enum: when watches go
synchronous this makes it easier (because then we have two reasons
to block)
Instead of using return value, use explicit state member inside
struct connection.
Signed-off-by: Rusty Russel <rusty@rustcorp.com.au>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>