make delay_tunnel consistent with delay_close

make delay_tunnel consistent with delay_close

1. Decrement counter on each mainloop iteration. Protocol needs to keep setting it to get more mainloop iterations before tunnel setup / close.
2. Value ≥2 causes us to set did_work=1, resulting in no delay before we call mainloop again. Protocol should only set this if it needs to SEND something in order to move things along.
3. Value =1 causes us to set did_work=0, resulting in a delay before we call mainloop again. Protocol should only set this if it needs to RECEIVE something in order to move things along.

Also fix values of NCP_TERM_ACK_{SENT,RECEIVED}.

Signed-off-by: Daniel Lenski <dlenski@gmail.com>