Draft: Always enqueue netmgr events

Previously, there was a microoptimization that would execute the requested event directly if the current thread would match the socket thread. With increasing numbers of networking threads, the benefit of doing so gets smaller, but the increased complexity in the source code stays the same. We remove the optimization for the sake of simplicity for the network manager design.

The only exception is udp_send() where it makes 5-6% difference in the performance.