This commit adds a new core header files `common/error.hpp` which
defines `ot::Error` (mirroring `otError`) and `kError{Name}` constants
(mirroring the public `OT_ERROR_{NAME}` definitions). The new (C++
style) definitions are used by core modules. This commit also moves
`otThreadErrorToString()` (from `logging.hpp` to `error.hpp`) and
renames it to `ErrorToString()` which is used as the internal (to
core) function to covert an `Error` to a string.
This commit introduces two configurations for Backbone Router to turn
off corresponding features:
- OPENTHREAD_CONFIG_BACKBONE_ROUTER_DUA_NDPROXYING_ENABLE: 1 by
default, set to 0 to disable Backbone Router DUA ND Proxying
- OPENTHREAD_CONFIG_BACKBONE_ROUTER_MULTICAST_ROUTING_ENABLE: 1 by
default, set to 0 to disable Backbone Router Multicast Routing
Both configuration requires OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE.
NOTE: At least one of these two configurations must be ON if
OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE=1(otherwise it's meaningless
to turn on OPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE).
Abtin Keshavarzian