Close iroh endpoing when stop_io() is called

[link2xt]

iOS is unhappy about open sockets when the app goes to background, including seemingly bound UDP sockets.

Instead of storing Endpoint in OnceCell, we should store it behind RwLock and Option:

deltachat-core-rust/src/context.rs

Line 295 in daeeca3

pub(crate) iroh: OnceCell<Iroh>,

Probably when I/O is restarted back we should restore the key and rejoin gossip, but as a first step we should drop everything and generate a new key each time I/O is restarted.

[Septias]

I can also do this if you want

[r10s]

it is already in progress at #6264

[Septias]

ah, didn't see the related PR

[gerryfrancis]

Now that #6264 has been merged, this issue should be closed, right?

[link2xt]

Closed by #6264