Avoid extending the base standard retransmission rules

[cabo@…]

Carsten Bormann notes:

Section 4.5

This paragraph (penultimate in 4.5) appears to be an opaque instruction to modify the algorithms in base core-coap:

The server SHOULD use a number of retransmit attempts (MAX_RETRANSMIT) such that removing a client from the list of observers before Max-Age ends is avoided.

This is surprising, because apart from this, -observe seems to be strictly in a using relationship to core-coap.

There may be interactions e.g. with MID lifetime ("retransmission window") that need to be carefully considered.

Also, continuing the BEBO (Binary Exponential Back-off) ad infinitum may not be the right approach; a truncated BEBO may be better.

Finally, this still has the maxage/pledge confusion that is being addressed by #204 and msg02898 and msg03073d.

[hartke@…]

Fixed in [1190]:

Closes #235