Revert "network.go:send(): retry and cleanup after fainures"

This reverts commit a7b5961cebcbb53c79fc43970735d9ff3eb20fa7.
Revert "fix connection establishment in high latency situations"

This reverts commit f7f218fc84883be5ad70cc701adf1091ec168849.
Fix tcp connection management for good

For each peer, keep at most one connection to which we write. Before a
connection can become a write connection, resend to it all messages the
previous one might have dropped.