fix(share/discovery): deadlock in limitedSet

[Wondertan]

Self-explanatory.

The deadlock eventually blocks the disconnect event processing in Discovery, causing libp2p connection processing to stall. Was discovered via libp2p metrics

[renaynay]

What was the reason for the ps.limit > 0 check inside of Remove anyway?

[Wondertan]

Because there is no reason to grow set indefinitely when limits is zero

[walldiss]

we need to release asap

[renaynay]

Eh weird @Wondertan - if discovery short-circuits bc peerslimit is 0, then Remove wouldn't even get called.

Anyway, approved

[Wondertan]

The surprising fact here is that I remember fixing this, and I even found a commit in revamp discovery PR 23b590e, and @vgonkivs pointed tp the deadlock. But somehow, it was removed afterward.

[Wondertan]

Eh weird @Wondertan - if discovery short-circuits bc peerslimit is 0, then Remove wouldn't even get called.

Yeah and there is no need to have that if, if that case is impossible

[Wondertan]

Found the commit which introduced the bug 82eb331.

Note that before that, I removed the if with lock(23b590e) completely in c5e0d00