* anders/diameter/spawn_opt/OTP-11299:
  Fix broken spawn_opt

* anders/diameter/failed_avp/OTP-11293:
  Fix Failed-AVP construction for CEA/DWA/DPA

Send of Failed-AVP resulted in encode failure.

The option was morphed into a boolean() and then ignored.

By using binary comprehensions. Add string-valued addresses to codec
suite.

The original code predates that module but there's no reason not to use
it now.

To accept any nested list of codepoints and binaries. A list containing
a binary was previously misinterpreted and the documentation was
incomplete.

Also, rework codec suite slightly to be able to specify values for which
decode o encode is the identity map, for which encode should succeed,
and for which encode should fail.

Having the peer_fsm process answer DWR meant that watchdog timer expiry
could result in an outgoing DWR despite the fact that an incoming DWR
was just answered. Having the watchdog process answer avoids this.

diameter_peer_fsm must be loaded before diameter_watchdog.  It's
possible for one incoming DWR to go unanswered but a subsequent DWR will
be answered so no harm is done.

Commit f0a36c79 broke the handling of such configuration, resulting in a
function clause error in diameter_capx if the list was not of length 3,
and faulty extraction of application id's otherwise.  Only record-valued
config was properly interpreted.