Close connection fast if both sides sent FIN

[cpq]

No description provided.

[robertc2000]

Looks good to me! I agree, if this improves performance, then we should close earlier.

[scaprile]

We can't set is_closing right away if dealing with TLS.
If the last segment we received had more than one TLS record, we need several calls to handle_tls_recv(c), so we must skip this if is_tls.
However, closure will only happen when the timeout expires, as we'll never revisit this.

Maybe we could do this check at mg_mgr_poll() along with c->is_tls && mg_tls_pending(c) > 0:

if (c->s->fin_rcvd && c->s->ttype == MIP_TTYPE_FIN) && (!c->is_tls || mg_tls_pending(c) <= 0))
      c->is_closing = true;