Fix broken spawn_opt

The option was morphed into a boolean() and then ignored.
Fix Failed-AVP construction for CEA/DWA/DPA

Send of Failed-AVP resulted in encode failure.
Merge branch 'anders/diameter/failed_avp/OTP-11293' into maint

* anders/diameter/failed_avp/OTP-11293:
  Fix Failed-AVP construction for CEA/DWA/DPA
Merge branch 'anders/diameter/spawn_opt/OTP-11299' into maint

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