Remove most special treatment for ifnet TLS in the TCP stack, except for code to avoid mixing handshakes and bulk data.

This code made heroic efforts to send down entire TLS records to NICs. It was added to improve the PCIe bus efficiency of older TLS offload NICs which did not keep state per-session, and so would need to re-DMA the first part(s) of a TLS record if a TLS record was sent in multiple TCP packets or TSOs. Newer TLS offload NICs do not need this feature.

At Netflix, we've run extensive QoE tests which show that this feature reduces client quality metrics, presumably because the effort to send TLS records atomically causes the server to both wait too long to send data (leading to buffers running dry), and to send too much data at once (leading to packet loss).