conn: Stop writing when our write bandwidth limist is exhausted
Commit 488e2b00 introduced an issue, most likely introduced by a bad copy paste, that made us stop reading on the connection if our write bandwidth limit was reached. The problem is that because "read_blocked_on_bw" was never set, the connection was never reenabled for reading. This is most likely the cause of #27813 where bytes were accumulating in the kernel TCP bufers because tor was not doing reads. Only relays with RelayBandwidthRate would suffer from this but affecting all relays connecting to them. And using that tor option is recommended and best practice so many many relays have it enabled. Fixes #28089.